In an isothermal process, applying an electric field E to a ferroelectric material can change its entropy S through two distinct mechanisms: namely, through changing the dipole alignment or configurational entropy (ΔSconf), and the vibrational entropy due to the intrinsic structure response (ΔSvib). Previous numerical investigations yield only the total entropy change ΔS but cannot separate these two contributions. Here we develop a full first-principles method to extract ΔSvib and the corresponding induced adiabatic temperature change ΔTvib under E, i.e. the electrocaloric effect (ECE), and compare them to the total ΔS and ΔT from molecular dynamics simulation based on a first-principles effective Hamiltonian model. For both single crystal PbTiO3 (PTO) and PbZr0.5Ti0.5O3 (50/50 PZT), the calculation results show that for T far from the phase transition temperature Tpt, ΔSvib plays an important and even dominant role in the ECE. On the other hand, for T close to Tpt, ΔSconf dominates the ECE. Moreover, for PTO, we find that positive E can cause positive ECE, while negative E cause negative ECE. Therefore, by combining both positive and negative ECE in a "bipolar" Ericsson cycle, the cooling energy density can significantly increase as compared to that of a unipolar cycle.
{"title":"The Ignored Effects of Vibrational Entropy and Electrocaloric Effect in PbTiO 3 and PbZr 0.5Ti 0.5O 3 as Studied Through First-Principles Calculation","authors":"Chenhan Liu, Wei Si, Chao Wu, Juekuan Yang, Yunfei Chen, C. Dames","doi":"10.2139/ssrn.3467755","DOIUrl":"https://doi.org/10.2139/ssrn.3467755","url":null,"abstract":"In an isothermal process, applying an electric field <i>E</i> to a ferroelectric material can change its entropy <i>S</i> through two distinct mechanisms: namely, through changing the dipole alignment or configurational entropy (<i>ΔS<sub>conf</sub></i>), and the vibrational entropy due to the intrinsic structure response (<i>ΔS<sub>vib</sub></i>). Previous numerical investigations yield only the total entropy change <i>ΔS</i> but cannot separate these two contributions. Here we develop a full first-principles method to extract <i>ΔS<sub>vib</sub></i> and the corresponding induced adiabatic temperature change <i>ΔT<sub>vib</sub></i> under <i>E</i>, i.e. the electrocaloric effect (ECE), and compare them to the total <i>ΔS</i> and <i>ΔT</i> from molecular dynamics simulation based on a first-principles effective Hamiltonian model. For both single crystal PbTiO<sub>3</sub> (PTO) and PbZr<sub>0.5</sub>Ti<sub>0.5</sub>O<sub>3</sub> (50/50 PZT), the calculation results show that for <i>T</i> far from the phase transition temperature <i>T<sub>pt</sub></i>, <i>ΔS<sub>vib</sub></i> plays an important and even dominant role in the ECE. On the other hand, for <i>T</i> close to <i>T<sub>pt</sub></i>, <i>ΔS<sub>conf</sub></i> dominates the ECE. Moreover, for PTO, we find that positive <i>E</i> can cause positive ECE, while negative <i>E</i> cause negative ECE. Therefore, by combining both positive and negative ECE in a \"bipolar\" Ericsson cycle, the cooling energy density can significantly increase as compared to that of a unipolar cycle.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"4 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82838408","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
T. Sawaguchi, W. Tasaki, I. Nikulin, Fumiyoshi Yoshinaka, S. Takamori, K. Tsuchiya, I. Kireeva, Y. Chumlyakov
Deformation-induced martensitic transformation from face-centred-cubic γ-austenite to hexagonal close-packed ε-martensite and body-centred-tetragonal α'-martensite has attracted much attention owing to the transformation-induced plasticity effect in austenitic stainless steels, high- and medium-Mn austenitic steels, ferrous shape memory alloys, and high entropy alloys. For better understanding of the complicated triple γ/ε/α' phase deformation microstructure, various structures at the intersection of different variants of deformation-induced ε-martensite are examined. A type-316 austenitic steel single crystal is compressively deformed along the [0 0 1]γ axis at a cryogenic temperature (173 K), and a deformation microstructure on the (1 1 0)γ surface is observed by means of scanning electron microscopy equipped with an electron backscattering diffraction analysis system. Depending on the shear angle with respect to the intersection axis, either 90º (Type I) or 30º (Type II), three types of atomic rearrangements of the intersection volume are observed: (1) reverse transformation into the γ-phase, which is rotated by 90º from the parent γ-austenite (Type I); (2) 10-12 twinning of either crossing ε-martensite variants (Type I); (3) secondary martensitic transformation into α'-martensite (Type II). Transformation matrices for the intersection products are built, which are then used to successfully calculate their crystallographic orientations starting from the orientation of the parent γ-phase. In addition, the atomic rearrangements and orientational changes are visualized by the distortion and/or kinking of Thompson's regular tetrahedron representing the initial atomic arrangement and the orientation of the parent γ-phase.
{"title":"Geometrical Models and Matrices for Structures at Intersection of Crossing ε-Martensite Variants","authors":"T. Sawaguchi, W. Tasaki, I. Nikulin, Fumiyoshi Yoshinaka, S. Takamori, K. Tsuchiya, I. Kireeva, Y. Chumlyakov","doi":"10.2139/ssrn.3436420","DOIUrl":"https://doi.org/10.2139/ssrn.3436420","url":null,"abstract":"Deformation-induced martensitic transformation from face-centred-cubic <i>γ</i>-austenite to hexagonal close-packed <i>ε</i>-martensite and body-centred-tetragonal <i>α'</i>-martensite has attracted much attention owing to the transformation-induced plasticity effect in austenitic stainless steels, high- and medium-Mn austenitic steels, ferrous shape memory alloys, and high entropy alloys. For better understanding of the complicated triple <i>γ/ε/α'</i> phase deformation microstructure, various structures at the intersection of different variants of deformation-induced ε-martensite are examined. A type-316 austenitic steel single crystal is compressively deformed along the [0 0 1]<sub>γ</sub> axis at a cryogenic temperature (173 K), and a deformation microstructure on the (1 1 0)<i>γ</i> surface is observed by means of scanning electron microscopy equipped with an electron backscattering diffraction analysis system. Depending on the shear angle with respect to the intersection axis, either 90º (Type I) or 30º (Type II), three types of atomic rearrangements of the intersection volume are observed: (1) reverse transformation into the <i>γ</i>-phase, which is rotated by 90º from the parent <i>γ</i>-austenite (Type I); (2) 10-12 twinning of either crossing <i>ε</i>-martensite variants (Type I); (3) secondary martensitic transformation into <i>α'</i>-martensite (Type II). Transformation matrices for the intersection products are built, which are then used to successfully calculate their crystallographic orientations starting from the orientation of the parent <i>γ</i>-phase. In addition, the atomic rearrangements and orientational changes are visualized by the distortion and/or kinking of Thompson's regular tetrahedron representing the initial atomic arrangement and the orientation of the parent <i>γ</i>-phase.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"5 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90966000","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
S. Irukuvarghula, H. Hassanin, C. Cayron, M. Aristizabal, Moataz M. Attallah, M. Preuss
Abstract The effect of powder size distribution and oxygen content on the extent of multiple twinning and spatial distribution of oxide inclusions in hot isostatic pressed (HIPed) 316L steels was investigated using powders with different characteristics. Modifications to, and differences in their microstructural topology, were tracked quantitatively by evaluating the metrics related to twin related domains (TRDs) on specimens produced by interrupting the HIPing process at various points in time. Results revealed that powder size distribution has a strong effect on the extent of multiple twinning in the fully HIPed microstructure, with specimens produced using narrow distribution showing better statistics (i.e., homogeneously recrystallized) than the ones produced using broad size distribution. The oxide inclusion density in fully HIPed microstructures increased with the amount of oxygen content in the powders while prior particle boundaries (PPBs) were only observed in the specimens that were HIPed using broad powder distribution. More importantly, results clearly revealed that the spatial distribution of the inclusions was strongly affected by the homogeneity of recrystallization. Implications of the results are further discussed in a broader context, emphasizing the importance of utilizing the occurrence of solid state phase transformations during HIPing for controlling the microstructure evolution.
{"title":"Effect of Powder Characteristics and Oxygen Content on Modifications to the Microstructural Topology During Hot Isostatic Pressing of an Austenitic Steel","authors":"S. Irukuvarghula, H. Hassanin, C. Cayron, M. Aristizabal, Moataz M. Attallah, M. Preuss","doi":"10.2139/ssrn.3299588","DOIUrl":"https://doi.org/10.2139/ssrn.3299588","url":null,"abstract":"Abstract The effect of powder size distribution and oxygen content on the extent of multiple twinning and spatial distribution of oxide inclusions in hot isostatic pressed (HIPed) 316L steels was investigated using powders with different characteristics. Modifications to, and differences in their microstructural topology, were tracked quantitatively by evaluating the metrics related to twin related domains (TRDs) on specimens produced by interrupting the HIPing process at various points in time. Results revealed that powder size distribution has a strong effect on the extent of multiple twinning in the fully HIPed microstructure, with specimens produced using narrow distribution showing better statistics (i.e., homogeneously recrystallized) than the ones produced using broad size distribution. The oxide inclusion density in fully HIPed microstructures increased with the amount of oxygen content in the powders while prior particle boundaries (PPBs) were only observed in the specimens that were HIPed using broad powder distribution. More importantly, results clearly revealed that the spatial distribution of the inclusions was strongly affected by the homogeneity of recrystallization. Implications of the results are further discussed in a broader context, emphasizing the importance of utilizing the occurrence of solid state phase transformations during HIPing for controlling the microstructure evolution.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"46 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2018-12-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83064313","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Anomalous basal stacking faults (SFs) have been frequently observed inside {10-11} and {10-12} twins in hexagonal close-packed metals. These SFs were first described by Song and Gray as "partial stacking faults" in the sense that only every other basal plane is displaced by the SFs. To further understand the formation mechanism of these SFs, in this work, we performed lattice correspondence analysis in the simulations of these two twinning modes. The corresponding plane of the parent to the prismatic plane of the twin was pre-selected and tracked before and after twinning. The atomic positions were closely examined to reveal the stacking sequence change in the twin due to the formation of the basal SFs. The results show that, indeed, only half of the atoms are displaced by the presence of the basal SFs, indicating that no global displacement vector can be defined and no dislocation activities are involved in the formation of the SFs. A special configuration of SFs was observed, which has limited mobility via coordinated atomic shuffles.
{"title":"Mechanism for the Formation of Partial Stacking Faults in Magnesium","authors":"Bin Li, Q. Sun, Qiwei Zhang, Xi-Yan Zhang","doi":"10.2139/ssrn.3289663","DOIUrl":"https://doi.org/10.2139/ssrn.3289663","url":null,"abstract":"Anomalous basal stacking faults (SFs) have been frequently observed inside {10-11} and {10-12} twins in hexagonal close-packed metals. These SFs were first described by Song and Gray as \"partial stacking faults\" in the sense that only every other basal plane is displaced by the SFs. To further understand the formation mechanism of these SFs, in this work, we performed lattice correspondence analysis in the simulations of these two twinning modes. The corresponding plane of the parent to the prismatic plane of the twin was pre-selected and tracked before and after twinning. The atomic positions were closely examined to reveal the stacking sequence change in the twin due to the formation of the basal SFs. The results show that, indeed, only half of the atoms are displaced by the presence of the basal SFs, indicating that no global displacement vector can be defined and no dislocation activities are involved in the formation of the SFs. A special configuration of SFs was observed, which has limited mobility via coordinated atomic shuffles.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"33 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2018-11-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85405673","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Linfeng zhou, Javad Samei, Jidong Kang, D. Wilkinson
We have investigated the effect of vanadium addition on a DP1300 ferrite-martensite steel, particularly in terms of microstructure, deformation, and damage behavior at the microscopic level. DP steels with and without vanadium addition were given slightly altered heat treatments to produce similar martensite content and ultimate tensile strength in both steels. The addition of 0.14wt% vanadium to the reference alloy yields a dispersion of nano-scale vanadium carbonitrides throughout the microstructure along with a pronounced grain refinement. Microscopic digital image correlation (μDIC) was employed to analyze the local strain partitioning between ferrite and martensite at the grain level. It was found that the addition of V increases the mechanical compatibility between ferrite and martensite. The consequent enhanced mechanical homogeneity and reduced strain gradients at the ferrite-martensite interface suppresses damage, thus enhancing ductility of the V-added alloy. Interrupted tensile tests coupled with X-ray computed tomography confirm that microstructural damage growth is slower in the V-added steel during post-uniform elongation prior to fracture.
{"title":"Influence of Vanadium on Microstrain Partitioning and Evolution of Microstructural Damage in DP1300 Steel","authors":"Linfeng zhou, Javad Samei, Jidong Kang, D. Wilkinson","doi":"10.2139/ssrn.3275443","DOIUrl":"https://doi.org/10.2139/ssrn.3275443","url":null,"abstract":"We have investigated the effect of vanadium addition on a DP1300 ferrite-martensite steel, particularly in terms of microstructure, deformation, and damage behavior at the microscopic level. DP steels with and without vanadium addition were given slightly altered heat treatments to produce similar martensite content and ultimate tensile strength in both steels. The addition of 0.14wt% vanadium to the reference alloy yields a dispersion of nano-scale vanadium carbonitrides throughout the microstructure along with a pronounced grain refinement. Microscopic digital image correlation (μDIC) was employed to analyze the local strain partitioning between ferrite and martensite at the grain level. It was found that the addition of V increases the mechanical compatibility between ferrite and martensite. The consequent enhanced mechanical homogeneity and reduced strain gradients at the ferrite-martensite interface suppresses damage, thus enhancing ductility of the V-added alloy. Interrupted tensile tests coupled with X-ray computed tomography confirm that microstructural damage growth is slower in the V-added steel during post-uniform elongation prior to fracture.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"7 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2018-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87189147","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Tao Liu, Zongrui Pei, Dallin J. Barton, Xuyang Zhou, G. Thompson, L. Brewer
Several interesting nanostructures of high pressure die cast A383 alloys were characterized via transmission electron microscopy (TEM) and atom probe tomography (APT). The refinement of the eutectic Si, which was caused by Sr addition, was found to be associated with the formation of nano-Al particles (~5 nm), with Cu partitioning (up to 5 at. %) at the Al/Si interface, within the eutectic Si. Direct observation of Sr segregation (0.4 at. %) was achieved at the interface between the eutectic Al and refined eutectic Si using APT. It is proposed that Sr refines the eutectic Si by restricting the growth of Si. Interestingly, the segregation of Mg (10.2 at. %) and Cu (0.9 at. %) is also present at the interface between the eutectic Al and the refined eutectic Si. Moreover, the presence of nano-Si particles (~20 nm) in the primary Al was characterized in the primary Al via APT. Segregations of Mg (2.9 at. %) and Cu (2.8 at. %) were also found at the interface between the primary Al and the nano-Si particles. Density functional theory (DFT) was used to assess the driving force for the segregation behavior of Cu and Mg at the Al/Si interface. DFT results also suggest that the segregation of Cu and Mg slightly decreases the cohesive energy of Al/Si interface but is a function of the length scale of the interface.
{"title":"Characterization of Nanostructures in the High Pressure Die Cast A383 Alloys","authors":"Tao Liu, Zongrui Pei, Dallin J. Barton, Xuyang Zhou, G. Thompson, L. Brewer","doi":"10.2139/ssrn.3892170","DOIUrl":"https://doi.org/10.2139/ssrn.3892170","url":null,"abstract":"Several interesting nanostructures of high pressure die cast A383 alloys were characterized via transmission electron microscopy (TEM) and atom probe tomography (APT). The refinement of the eutectic Si, which was caused by Sr addition, was found to be associated with the formation of nano-Al particles (~5 nm), with Cu partitioning (up to 5 at. %) at the Al/Si interface, within the eutectic Si. Direct observation of Sr segregation (0.4 at. %) was achieved at the interface between the eutectic Al and refined eutectic Si using APT. It is proposed that Sr refines the eutectic Si by restricting the growth of Si. Interestingly, the segregation of Mg (10.2 at. %) and Cu (0.9 at. %) is also present at the interface between the eutectic Al and the refined eutectic Si. Moreover, the presence of nano-Si particles (~20 nm) in the primary Al was characterized in the primary Al via APT. Segregations of Mg (2.9 at. %) and Cu (2.8 at. %) were also found at the interface between the primary Al and the nano-Si particles. Density functional theory (DFT) was used to assess the driving force for the segregation behavior of Cu and Mg at the Al/Si interface. DFT results also suggest that the segregation of Cu and Mg slightly decreases the cohesive energy of Al/Si interface but is a function of the length scale of the interface.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"10 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"1993-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87078138","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
F. Dong, J. Venezuela, Huixing Li, Z. Shi, Qingjun Zhou, Lian-sheng Chen, J. Chen, L. Du, A. Atrens
The hydrogen embrittlement (HE) of some DP steels was investigated, focusing on the influence of the phosphorus (P) content. Hydrogen-induced micro-cracks and brittle fracture occurred at edges follows the HESIV and HEDE mechanisms. The increased number of ferrite related interface micro-cracks was attributed by the enhanced interface weakening effect of excess P content. Hydrogen influenced crack propagation and fracture in the inner ductile part of the specimen followed the HELP mechanism and can be promoted by a higher P content in solution in matrix. An increased P content caused more significant HE susceptibility for DP steel with less and separated martensite and less Cr, Mo microalloying.
{"title":"Influence of the Phosphorus Content on the Hydrogen Embrittlement Susceptibility of Some DP Steels Studied Using the Linearly Increasing Stress Test","authors":"F. Dong, J. Venezuela, Huixing Li, Z. Shi, Qingjun Zhou, Lian-sheng Chen, J. Chen, L. Du, A. Atrens","doi":"10.2139/ssrn.3883350","DOIUrl":"https://doi.org/10.2139/ssrn.3883350","url":null,"abstract":"The hydrogen embrittlement (HE) of some DP steels was investigated, focusing on the influence of the phosphorus (P) content. Hydrogen-induced micro-cracks and brittle fracture occurred at edges follows the HESIV and HEDE mechanisms. The increased number of ferrite related interface micro-cracks was attributed by the enhanced interface weakening effect of excess P content. Hydrogen influenced crack propagation and fracture in the inner ductile part of the specimen followed the HELP mechanism and can be promoted by a higher P content in solution in matrix. An increased P content caused more significant HE susceptibility for DP steel with less and separated martensite and less Cr, Mo microalloying.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"36 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80141580","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Qiyang Tan, Yu Yin, Feng Wang, Shiyang Liu, A. Prasad, W. Qu, Gan Li, Tao Wu, Jingqi Zhang, Yingang Liu, Xianliang Yang, Q. Zhu, D. St John, Mingxing Zhang
Grain refinement is one of the most effective approaches to improving mechanical properties, reducing anisotropy and hot-cracking of additively manufactured alloys. Recent studies have shown that the extreme solidification conditions associated with additive manufacturing (AM), including large thermal gradient and rapid cooling rate, result in the difference in nucleation and grain growth mechanisms between AM and conventional casting. Thus, it is necessary to re-consider the grain refinement mechanisms, particularly the role of solute during AM. The present work investigates the grain refining efficiencies of different solute additives (Si, Cu and Ni) and their integration with nucleants (LaB6 nanoparticles) in additively manufactured pure Al. It was found that, despite the rapid cooling during AM and nucleant inoculation, solute addition is essential for activating heterogeneous nucleation upon solidification to achieve high grain refining efficiency. However, the role of solute in grain refinement during AM cannot be readily interpreted by the classic grain growth restriction theory (Q value). This is attributed to the large thermal gradient in the melt pools during AM solidification, which significantly limits the development of constitutional supercooling. Alternatively, the role of solute can be better understood in terms of the lag in dendrite growth induced by solute rejection during solidification. This causes the difference between the actual dendrite growth and the theoretical pull rate, generating large thermal undercooling at the solidification front to elicit heterogeneous nucleation. This work sheds new light on the factors affecting grain refinement under rapid solidification.
{"title":"Uncovering the Role of Solute in Grain Refinement of Additively Manufactured Aluminium Alloys","authors":"Qiyang Tan, Yu Yin, Feng Wang, Shiyang Liu, A. Prasad, W. Qu, Gan Li, Tao Wu, Jingqi Zhang, Yingang Liu, Xianliang Yang, Q. Zhu, D. St John, Mingxing Zhang","doi":"10.2139/ssrn.3869172","DOIUrl":"https://doi.org/10.2139/ssrn.3869172","url":null,"abstract":"Grain refinement is one of the most effective approaches to improving mechanical properties, reducing anisotropy and hot-cracking of additively manufactured alloys. Recent studies have shown that the extreme solidification conditions associated with additive manufacturing (AM), including large thermal gradient and rapid cooling rate, result in the difference in nucleation and grain growth mechanisms between AM and conventional casting. Thus, it is necessary to re-consider the grain refinement mechanisms, particularly the role of solute during AM. The present work investigates the grain refining efficiencies of different solute additives (Si, Cu and Ni) and their integration with nucleants (LaB6 nanoparticles) in additively manufactured pure Al. It was found that, despite the rapid cooling during AM and nucleant inoculation, solute addition is essential for activating heterogeneous nucleation upon solidification to achieve high grain refining efficiency. However, the role of solute in grain refinement during AM cannot be readily interpreted by the classic grain growth restriction theory (Q value). This is attributed to the large thermal gradient in the melt pools during AM solidification, which significantly limits the development of constitutional supercooling. Alternatively, the role of solute can be better understood in terms of the lag in dendrite growth induced by solute rejection during solidification. This causes the difference between the actual dendrite growth and the theoretical pull rate, generating large thermal undercooling at the solidification front to elicit heterogeneous nucleation. This work sheds new light on the factors affecting grain refinement under rapid solidification.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"55 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74587600","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Apurv Dash, J. Malzbender, M. Rasinski, O. Guillon, Jesus Julian Gonzalez
The sintering and simultaneous texturing of Ti3SiC2 MAX phase ceramics have been reported. The degree of orientation of Ti3SiC2 grains were quantified with X-ray diffraction for the bulk crystallographic texture and electron back scattered diffraction for local and morphological texture. Analysis revealed that the basal plane of Ti3SiC2 was aligned perpendicular to the direction of applied external force during sintering. The textured MAX phase was subjected to high temperature annealing to induce grain growth which resulted in a duplex microstructure. The ceramics with fine (~1 µm) and duplex (500 µm wide elongated grains in a matrix of equiaxed 1 µm grains) microstructure were subjected to compressive creep tests at high temperature (1000-1300 °C) in different directions with respect the orientation of the crystals in the bulk Ti3SiC2. The creep resistance was highest for fine grained Ti3SiC2 with basal planes aligned perpendicular to the direction of applied stress, whereas the ceramics with duplex microstructure and basal plane aligned parallel to the direction of applied stress suffered the highest creep deformation. A probable mechanism for the creep response of the different grades of Ti3SiC2 has been proposed.
{"title":"Effect of Texture and Grain Size on the Compressive Creep of Ti 3SiC 2 MAX Phase Ceramics","authors":"Apurv Dash, J. Malzbender, M. Rasinski, O. Guillon, Jesus Julian Gonzalez","doi":"10.2139/ssrn.3883352","DOIUrl":"https://doi.org/10.2139/ssrn.3883352","url":null,"abstract":"The sintering and simultaneous texturing of Ti<sub>3</sub>SiC<sub>2</sub> MAX phase ceramics have been reported. The degree of orientation of Ti<sub>3</sub>SiC<sub>2</sub> grains were quantified with X-ray diffraction for the bulk crystallographic texture and electron back scattered diffraction for local and morphological texture. Analysis revealed that the basal plane of Ti<sub>3</sub>SiC<sub>2</sub> was aligned perpendicular to the direction of applied external force during sintering. The textured MAX phase was subjected to high temperature annealing to induce grain growth which resulted in a duplex microstructure. The ceramics with fine (~1 µm) and duplex (500 µm wide elongated grains in a matrix of equiaxed 1 µm grains) microstructure were subjected to compressive creep tests at high temperature (1000-1300 °C) in different directions with respect the orientation of the crystals in the bulk Ti<sub>3</sub>SiC<sub>2</sub>. The creep resistance was highest for fine grained Ti<sub>3</sub>SiC<sub>2</sub> with basal planes aligned perpendicular to the direction of applied stress, whereas the ceramics with duplex microstructure and basal plane aligned parallel to the direction of applied stress suffered the highest creep deformation. A probable mechanism for the creep response of the different grades of Ti<sub>3</sub>SiC<sub>2</sub> has been proposed.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"93 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74171712","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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