Pub Date : 2002-02-01DOI: 10.2320/MATERTRANS.43.182
M. Hirscher, M. Ege
High-purity FeCr single crystals with Cr contents between 34 at% and 60 at% and orientations close to the direction were prepared by containerless inductive zone melting under Ar atmosphere. The internal friction was measured between temperatures of 300 to 1200 K using an inverted torsion pendulum in the frequency range between 2 and 80 Hz. A strong damping is observed below the Curie temperature due to domain wall motion. Above the ferromagnetic transition temperature a relaxation maximum occurs at about 950 K. This relaxation can be assigned to the so-called Zener relaxation which is due to the stress-induced reorientation of short-range ordered Fe and Cr atoms, respectively. An analysis yielded an effective activation enthalpy of (3.1 ± 0.3) eV showing no significant dependence on the composition. The relaxation strength shows a maximum value near the equiatomic composition and decreases for lower and higher Cr contents. Furthermore, the influence of the a phase on the internal friction and the dynamic torsional shear modulus was studied on a single crystal with a Cr content of 48 at%. After annealing for 24 h at 973 K the torsional shear modulus increases with temperature up to over 1000K, indicating a hardening due to precipitates of the a phase.
{"title":"Composition dependence of the Zener relaxation in high-purity FeCr single crystals","authors":"M. Hirscher, M. Ege","doi":"10.2320/MATERTRANS.43.182","DOIUrl":"https://doi.org/10.2320/MATERTRANS.43.182","url":null,"abstract":"High-purity FeCr single crystals with Cr contents between 34 at% and 60 at% and orientations close to the direction were prepared by containerless inductive zone melting under Ar atmosphere. The internal friction was measured between temperatures of 300 to 1200 K using an inverted torsion pendulum in the frequency range between 2 and 80 Hz. A strong damping is observed below the Curie temperature due to domain wall motion. Above the ferromagnetic transition temperature a relaxation maximum occurs at about 950 K. This relaxation can be assigned to the so-called Zener relaxation which is due to the stress-induced reorientation of short-range ordered Fe and Cr atoms, respectively. An analysis yielded an effective activation enthalpy of (3.1 ± 0.3) eV showing no significant dependence on the composition. The relaxation strength shows a maximum value near the equiatomic composition and decreases for lower and higher Cr contents. Furthermore, the influence of the a phase on the internal friction and the dynamic torsional shear modulus was studied on a single crystal with a Cr content of 48 at%. After annealing for 24 h at 973 K the torsional shear modulus increases with temperature up to over 1000K, indicating a hardening due to precipitates of the a phase.","PeriodicalId":18264,"journal":{"name":"Materials Transactions Jim","volume":"1 1","pages":"182-185"},"PeriodicalIF":0.0,"publicationDate":"2002-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88347887","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}
Pub Date : 2001-12-01DOI: 10.2320/MATERTRANS.42.2511
Tzong H. Chen, John Dutrizac
A stockpiled zinc ferrite residue from Noranda Inc., CEZinc consists mostly of ZnFe 2 O 4 and Fe 2 O 3 , together with trace amounts of a number of other phases including Mn-bearing oxides and Sr sulphate. Reductive roasting of the zinc ferrite residue for 2 h at 800°C resulted in the extensive conversion of the ZnFe 2 O 4 to (Fe, Zn)O and ZnO; the (Fe, Zn)O phase contains about 16 mass%Zn. The particle sizes and shapes after reductive roasting are similar to those in the unroasted feed, but the roasted material may be slightly more porous. The copper impurity in the ferrite residue is reduced to an Ag-bearing copper alloy which occurs as inclusions along the grain boundaries of the (Fe, Zn)O phase. Some of the Sr sulphate present in the zinc ferrite residue is reduced to a Zn-Fe-Sr sulphide phase, and all of the initially present Fe 2 O 3 is reduced to (Fe, Zn)O. Reductive roasting converts the zinc ferrite residue into species which are soluble in dilute acid or alkaline media, thereby allowing the potential recycling of the Zn, Cu and Ag values.
{"title":"A mineralogical study of the reductive roasting of zinc ferrite residues: A potential zinc recycling technology : Special issue on recycling and high performance waste processing","authors":"Tzong H. Chen, John Dutrizac","doi":"10.2320/MATERTRANS.42.2511","DOIUrl":"https://doi.org/10.2320/MATERTRANS.42.2511","url":null,"abstract":"A stockpiled zinc ferrite residue from Noranda Inc., CEZinc consists mostly of ZnFe 2 O 4 and Fe 2 O 3 , together with trace amounts of a number of other phases including Mn-bearing oxides and Sr sulphate. Reductive roasting of the zinc ferrite residue for 2 h at 800°C resulted in the extensive conversion of the ZnFe 2 O 4 to (Fe, Zn)O and ZnO; the (Fe, Zn)O phase contains about 16 mass%Zn. The particle sizes and shapes after reductive roasting are similar to those in the unroasted feed, but the roasted material may be slightly more porous. The copper impurity in the ferrite residue is reduced to an Ag-bearing copper alloy which occurs as inclusions along the grain boundaries of the (Fe, Zn)O phase. Some of the Sr sulphate present in the zinc ferrite residue is reduced to a Zn-Fe-Sr sulphide phase, and all of the initially present Fe 2 O 3 is reduced to (Fe, Zn)O. Reductive roasting converts the zinc ferrite residue into species which are soluble in dilute acid or alkaline media, thereby allowing the potential recycling of the Zn, Cu and Ag values.","PeriodicalId":18264,"journal":{"name":"Materials Transactions Jim","volume":"65 6 Pt B 1","pages":"2511-2518"},"PeriodicalIF":0.0,"publicationDate":"2001-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77017377","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}
Pub Date : 2001-12-01DOI: 10.2320/MATERTRANS.42.2492
R. Suzuki, A. Saguchi, W. Takahashi, T. Yagura, K. Ono
Powder scraps of neodymium-iron-boron permanent magnet were deoxidized by using calcium vapor, liquid or CaCl 2 melt at 1223-1273 K. Because the scraps react with the acidic solutions during leaching of the byproduct CaO, the methods for removal of the excess amount of Ca and CaO were studied. When pH was controlled at about 8 during several times leaching, the dissolution of rare earth elements could be minimized. Ca vapor deoxidation could not supply enough amount of Ca through CaO layer. When a large amount of CaCl 2 was added, the dissolution rate of CaO into the aqueous solution became faster, but some amounts of rare earth components were lost. The deoxidation by Ca liquid and 5 mass%CaCl 2 and the subsequent leaching in distilled water with pH > 8 gave the better result so that oxygen, even in heavily oxidized scraps, could be lowered to 0.7 mass%.
{"title":"Recycling of rare earth magnet scraps: Part II Oxygen removal by calcium : Special issue on recycling and high performance waste processing","authors":"R. Suzuki, A. Saguchi, W. Takahashi, T. Yagura, K. Ono","doi":"10.2320/MATERTRANS.42.2492","DOIUrl":"https://doi.org/10.2320/MATERTRANS.42.2492","url":null,"abstract":"Powder scraps of neodymium-iron-boron permanent magnet were deoxidized by using calcium vapor, liquid or CaCl 2 melt at 1223-1273 K. Because the scraps react with the acidic solutions during leaching of the byproduct CaO, the methods for removal of the excess amount of Ca and CaO were studied. When pH was controlled at about 8 during several times leaching, the dissolution of rare earth elements could be minimized. Ca vapor deoxidation could not supply enough amount of Ca through CaO layer. When a large amount of CaCl 2 was added, the dissolution rate of CaO into the aqueous solution became faster, but some amounts of rare earth components were lost. The deoxidation by Ca liquid and 5 mass%CaCl 2 and the subsequent leaching in distilled water with pH > 8 gave the better result so that oxygen, even in heavily oxidized scraps, could be lowered to 0.7 mass%.","PeriodicalId":18264,"journal":{"name":"Materials Transactions Jim","volume":"11 1","pages":"2492-2498"},"PeriodicalIF":0.0,"publicationDate":"2001-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84031883","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}
Pub Date : 2001-12-01DOI: 10.2320/MATERTRANS.42.2487
Kazutaka Asabe, A. Saguchi, W. Takahashi, R. Suzuki, K. Ono
In the recycling of the permanent Nd-Fe-B magnet, the carbon such as free carbon and carbides at the grain boundary segregation in the magnet scrap are elements that are harmful and which obstruct the magnet performance. The removal of the carbon is currently a major problem. Remelting of scraps should, therefore, be done on condition that the carbon content is lowered to an appropriate level prior to melting. The aim of this work was to open the route for decarburization of the Nd magnet powder scraps with high carbon, as well as of the sintered body scraps with moderate carbon concentration. Decarburization via oxidation in air allowed the removal of not only free carbon but also grain boundary carbides at temperatures higher than 1273 K down to 300 mass ppm. However, an increase in the oxygen content is inevitable with the high temperature oxidation. The next step was then to reduce the iron oxide by heating it in a hydrogen atmosphere at 1273 K and subsequently to eliminate the oxygen combined with the rare-earth constituent using calcium which has a strong affinity with oxygen. The basic technology for the recycling process of the permanent Nd-Fe-B magnet scraps was discussed.
{"title":"Recycling of rare earth magnet scraps: Part I Carbon removal by high temperature oxidation : Special issue on recycling and high performance waste processing","authors":"Kazutaka Asabe, A. Saguchi, W. Takahashi, R. Suzuki, K. Ono","doi":"10.2320/MATERTRANS.42.2487","DOIUrl":"https://doi.org/10.2320/MATERTRANS.42.2487","url":null,"abstract":"In the recycling of the permanent Nd-Fe-B magnet, the carbon such as free carbon and carbides at the grain boundary segregation in the magnet scrap are elements that are harmful and which obstruct the magnet performance. The removal of the carbon is currently a major problem. Remelting of scraps should, therefore, be done on condition that the carbon content is lowered to an appropriate level prior to melting. The aim of this work was to open the route for decarburization of the Nd magnet powder scraps with high carbon, as well as of the sintered body scraps with moderate carbon concentration. Decarburization via oxidation in air allowed the removal of not only free carbon but also grain boundary carbides at temperatures higher than 1273 K down to 300 mass ppm. However, an increase in the oxygen content is inevitable with the high temperature oxidation. The next step was then to reduce the iron oxide by heating it in a hydrogen atmosphere at 1273 K and subsequently to eliminate the oxygen combined with the rare-earth constituent using calcium which has a strong affinity with oxygen. The basic technology for the recycling process of the permanent Nd-Fe-B magnet scraps was discussed.","PeriodicalId":18264,"journal":{"name":"Materials Transactions Jim","volume":"236 2 1","pages":"2487-2491"},"PeriodicalIF":0.0,"publicationDate":"2001-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85653379","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}
Pub Date : 2001-12-01DOI: 10.2320/MATERTRANS.42.2519
Liu Kejun, A. Shibayama, W. Yen, T. Miyazaki, T. Fujita, K. Murata
The extraction Au, Pd, Ag and Cu from electronic disposed portable telephone fragmented by explosive in water using several leaching solution was studied in this investigation. The metals extraction by three kinds of leaching solution, thiosulfate, iodine, and aqua regia, were compared. The best metals extraction was obtained from a 30 mass% aqua regia solution. The efficiency of metals extraction from the samples fragmented in different extents was compared with the 10 mass% aqua regia solution. The recovery of 91.97% Au, 97.69% Pd and 90.87% Cu could be achieved by a 30 mass% aqua regia solution at the retention of 54 h.
{"title":"Extraction of metals from disposed fragmented portable telephones by various leaching solution : Special issue on recycling and high performance waste processing","authors":"Liu Kejun, A. Shibayama, W. Yen, T. Miyazaki, T. Fujita, K. Murata","doi":"10.2320/MATERTRANS.42.2519","DOIUrl":"https://doi.org/10.2320/MATERTRANS.42.2519","url":null,"abstract":"The extraction Au, Pd, Ag and Cu from electronic disposed portable telephone fragmented by explosive in water using several leaching solution was studied in this investigation. The metals extraction by three kinds of leaching solution, thiosulfate, iodine, and aqua regia, were compared. The best metals extraction was obtained from a 30 mass% aqua regia solution. The efficiency of metals extraction from the samples fragmented in different extents was compared with the 10 mass% aqua regia solution. The recovery of 91.97% Au, 97.69% Pd and 90.87% Cu could be achieved by a 30 mass% aqua regia solution at the retention of 54 h.","PeriodicalId":18264,"journal":{"name":"Materials Transactions Jim","volume":"28 1","pages":"2519-2522"},"PeriodicalIF":0.0,"publicationDate":"2001-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81535284","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}
Pub Date : 2001-11-20DOI: 10.2320/MATERTRANS.42.2232
T. Fukuda, M. Hida, A. Sakakibara, Y. Takemoto
The bonding state has been studied by the discrete variational (DV)-Xa method in the vicinity of the core of the Peierls-Nabarro edge dislocation in the BCC(Fe) crystal the slip systems of which are {112}(111) and [110](111). Bond order and net charge distribution were evaluated in the perfect crystal model cluster and edge dislocation core model cluster with 32 atoms. In the {112}(111) slip system, the total bond order of the nearest neighbor atom pairs in the dislocation model was found to be relatively larger than that in the perfect crystal model. On the other hand, the total bond order of the second neighbor atom pairs in the dislocation model was a little smaller than that in the perfect crystal model. It was also found that there was asymmetry in the bond order between the (110) plane on the left side and the one on the right side of the (110) plane which contains the core atom of dislocation. Net charge and its effect in the dislocation model were larger and wider than those in the perfect crystal model. Almost the same results were also attained for the {110}(111) slip system.
{"title":"Evaluation of bonding state of BCC(Fe) edge dislocation core by DV-Xα cluster method : Advances in computational materials science and engineering II","authors":"T. Fukuda, M. Hida, A. Sakakibara, Y. Takemoto","doi":"10.2320/MATERTRANS.42.2232","DOIUrl":"https://doi.org/10.2320/MATERTRANS.42.2232","url":null,"abstract":"The bonding state has been studied by the discrete variational (DV)-Xa method in the vicinity of the core of the Peierls-Nabarro edge dislocation in the BCC(Fe) crystal the slip systems of which are {112}(111) and [110](111). Bond order and net charge distribution were evaluated in the perfect crystal model cluster and edge dislocation core model cluster with 32 atoms. In the {112}(111) slip system, the total bond order of the nearest neighbor atom pairs in the dislocation model was found to be relatively larger than that in the perfect crystal model. On the other hand, the total bond order of the second neighbor atom pairs in the dislocation model was a little smaller than that in the perfect crystal model. It was also found that there was asymmetry in the bond order between the (110) plane on the left side and the one on the right side of the (110) plane which contains the core atom of dislocation. Net charge and its effect in the dislocation model were larger and wider than those in the perfect crystal model. Almost the same results were also attained for the {110}(111) slip system.","PeriodicalId":18264,"journal":{"name":"Materials Transactions Jim","volume":"56 1","pages":"2232-2237"},"PeriodicalIF":0.0,"publicationDate":"2001-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90484168","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}
Pub Date : 2001-11-20DOI: 10.2320/MATERTRANS.42.2206
T. Hoshino, Toshiya Mizuno, M. Asato, H. Fukushima
We present systematic first-principles calculations for vacancy formation energies E F V in most of elemental metals (Li∼Au) of fcc and bcc structures, as well as hulk properties such as lattice parameters a and bulk moduli B. The calculations are based on the generalized-gradient approximation in density-functional formalism, proposed by Perdew and Wang in 1991 (PW91-GGA), and apply the full-potential Korringa-Kohn-Rostoker Green's function method for perfect crystals and point defect systems, developed by the Julich group. First we show that the calculated hulk properties for all elements studied are in excellent agreement with the experimental results: the PW91-GGA corrects the deficiencies of the local spin density approximation for metals, i.e., the underestimation of o and the overestimation of B and the theoretical errors in a and B are reduced within ∼ 1% and ∼ 10% of experimental results, respectively. Second we show that E F V for most of fcc metals are reproduced within the experimental errors, while E F V for most of bcc metals are overestimated by 10%-20% of the experimental results. It is noted that the comparison with the experimental results needs the inclusion of the thermal lattice expansion effect in the first-principles calculations because most of the experimental results were derived from positron annihilation measurements at high temperatures. The remaining discrepancies between theory and experiment are also discussed.
我们提出系统采用基于计算空位形成能量E V F在大多数金属元素(李∼Au) fcc, bcc结构,以及绿巨人属性比如晶格参数和体积模b .广义梯度近似的计算是基于密度泛函形式主义,Perdew和王在1991年提出的(PW91-GGA)和应用潜力Korringa-Kohn-Rostoker格林函数方法,完美晶体和点缺陷系统,由Julich集团开发。首先，我们证明了所研究的所有元素的计算体积性质与实验结果非常吻合:PW91-GGA纠正了金属局部自旋密度近似的缺陷，即对0的低估和对B的高估，a和B的理论误差分别减少到实验结果的1%和10%以内。其次，我们表明，大多数fcc金属的E - F - V在实验误差范围内可以再现，而大多数bcc金属的E - F - V被高估了实验结果的10%-20%。由于大多数实验结果来自于高温下的正电子湮灭测量，因此与实验结果的比较需要在第一性原理计算中包含热晶格膨胀效应。本文还讨论了理论与实验之间的差异。
{"title":"Full-potential KKR calculations for point defect energies in metals, based on the generalized-gradient approximation: I. Vacancy formation energies in fcc and bcc metals : Advances in computational materials science and engineering II","authors":"T. Hoshino, Toshiya Mizuno, M. Asato, H. Fukushima","doi":"10.2320/MATERTRANS.42.2206","DOIUrl":"https://doi.org/10.2320/MATERTRANS.42.2206","url":null,"abstract":"We present systematic first-principles calculations for vacancy formation energies E F V in most of elemental metals (Li∼Au) of fcc and bcc structures, as well as hulk properties such as lattice parameters a and bulk moduli B. The calculations are based on the generalized-gradient approximation in density-functional formalism, proposed by Perdew and Wang in 1991 (PW91-GGA), and apply the full-potential Korringa-Kohn-Rostoker Green's function method for perfect crystals and point defect systems, developed by the Julich group. First we show that the calculated hulk properties for all elements studied are in excellent agreement with the experimental results: the PW91-GGA corrects the deficiencies of the local spin density approximation for metals, i.e., the underestimation of o and the overestimation of B and the theoretical errors in a and B are reduced within ∼ 1% and ∼ 10% of experimental results, respectively. Second we show that E F V for most of fcc metals are reproduced within the experimental errors, while E F V for most of bcc metals are overestimated by 10%-20% of the experimental results. It is noted that the comparison with the experimental results needs the inclusion of the thermal lattice expansion effect in the first-principles calculations because most of the experimental results were derived from positron annihilation measurements at high temperatures. The remaining discrepancies between theory and experiment are also discussed.","PeriodicalId":18264,"journal":{"name":"Materials Transactions Jim","volume":"64 1","pages":"2206-2215"},"PeriodicalIF":0.0,"publicationDate":"2001-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90495835","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}
Pub Date : 2001-11-20DOI: 10.2320/MATERTRANS.42.2279
S. Vannarat, K. Esfarjani, S. Chui, Y. Kawazoe
Self-assembled islands are spontaneously formed during the heteroepitaxial growth of InAs on GaAs substrate. The island formation creates strain fields in the substrate and this leads to elastic interaction between the islands. We calculate the strain energy of the array of InAs islands on the GaAs substrate by the finite element method, and extract the elastic interaction between the islands from the variation of the energy with the distance between the islands. The interaction decays with the third power of the inter-island distance, in agreement with our previous work. The effect of the interaction on the correlation of the island positions is examined by comparing the coefficient of the interaction with the phase transition criteria of the two-dimensional dipole system. When the island size is large enough, depending on the island density, an array of islands can be in either a liquid phase where the islands are randomly distributed or in a solid phase where the islands form a two dimensional lattice. Only the liquid phase exists when the island size is small.
{"title":"Effect of elastic interaction on self-assembled island spatial arrangement : Advances in computational materials science and engineering II","authors":"S. Vannarat, K. Esfarjani, S. Chui, Y. Kawazoe","doi":"10.2320/MATERTRANS.42.2279","DOIUrl":"https://doi.org/10.2320/MATERTRANS.42.2279","url":null,"abstract":"Self-assembled islands are spontaneously formed during the heteroepitaxial growth of InAs on GaAs substrate. The island formation creates strain fields in the substrate and this leads to elastic interaction between the islands. We calculate the strain energy of the array of InAs islands on the GaAs substrate by the finite element method, and extract the elastic interaction between the islands from the variation of the energy with the distance between the islands. The interaction decays with the third power of the inter-island distance, in agreement with our previous work. The effect of the interaction on the correlation of the island positions is examined by comparing the coefficient of the interaction with the phase transition criteria of the two-dimensional dipole system. When the island size is large enough, depending on the island density, an array of islands can be in either a liquid phase where the islands are randomly distributed or in a solid phase where the islands form a two dimensional lattice. Only the liquid phase exists when the island size is small.","PeriodicalId":18264,"journal":{"name":"Materials Transactions Jim","volume":"3 1 1","pages":"2279-2282"},"PeriodicalIF":0.0,"publicationDate":"2001-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82230583","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}
Pub Date : 2001-11-20DOI: 10.2320/MATERTRANS.42.2283
Xuejun Xu, M. Wen, S. Fukuyama, K. Yokogawa
A molecular dynamics simulation by the embedded atom method was conducted to investigate hydrogen embrittlement of a nickel single crystal, which is composed of 163311 nickel atoms on the nanometer scale and has a [011]-oriented notch under uniaxial tension along the [100] direction at room temperature. The hydrogen-free specimen showed good ductility associated with pronounced blunting of the crack tip. Hydrogen influence was most serious in the specimen that had been hydrogen-charged in the notched (100) planes ahead of the crack tip. In the specimen that had been hydrogen-charged in the notched area, a hydrogen-assisted fracture occurred macroscopically on the (100) plane perpendicular to the tensile direction and the elongation at failure decreased with increasing hydrogen content. A low hydrogen content caused strain localization only, while a high hydrogen content caused microvoid formation in the notched area as well. The specimen containing a thin layer of hydride fractured and exhibited brittleness due to significant microvoid formation and subsequent microvoid growth and linkage at the early stage of deformation. The simulation results show good agreement with the published experimental observations.
{"title":"Simulation of hydrogen embrittlement at crack tip in nickel single crystal by embedded atom method : Advances in computational materials science and engineering II","authors":"Xuejun Xu, M. Wen, S. Fukuyama, K. Yokogawa","doi":"10.2320/MATERTRANS.42.2283","DOIUrl":"https://doi.org/10.2320/MATERTRANS.42.2283","url":null,"abstract":"A molecular dynamics simulation by the embedded atom method was conducted to investigate hydrogen embrittlement of a nickel single crystal, which is composed of 163311 nickel atoms on the nanometer scale and has a [011]-oriented notch under uniaxial tension along the [100] direction at room temperature. The hydrogen-free specimen showed good ductility associated with pronounced blunting of the crack tip. Hydrogen influence was most serious in the specimen that had been hydrogen-charged in the notched (100) planes ahead of the crack tip. In the specimen that had been hydrogen-charged in the notched area, a hydrogen-assisted fracture occurred macroscopically on the (100) plane perpendicular to the tensile direction and the elongation at failure decreased with increasing hydrogen content. A low hydrogen content caused strain localization only, while a high hydrogen content caused microvoid formation in the notched area as well. The specimen containing a thin layer of hydride fractured and exhibited brittleness due to significant microvoid formation and subsequent microvoid growth and linkage at the early stage of deformation. The simulation results show good agreement with the published experimental observations.","PeriodicalId":18264,"journal":{"name":"Materials Transactions Jim","volume":"7 1","pages":"2283-2289"},"PeriodicalIF":0.0,"publicationDate":"2001-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87132195","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}
Pub Date : 2001-11-20DOI: 10.2320/MATERTRANS.42.2157
V. Matić, L. Wille, N. Lazarov, M. Milic
We Study the low-temperature thermodynamical and statistical properties of the ASYNNNI model, used to describe oxygen ordering in YBa 2 Cu 3 O 6+2c . Analyzing the excited states we show that this model undergoes a second order phase transition at absolute zero temperature. From the divergence of the relative energy fluctuations, in the limit T → 0, we deduce that for T 0 the deviation of the chemical potential μ from its ground state value is linearly related to the partial derivative of the fraction of threefold coordinated Cu(1) ions n with respect to oxygen concentlation c. We use the cluster variation method (CVM) to determine the numerical value of the coefficient of this relation and find that it is equal to -1/2, independently of the values of the interaction parameters. This establishes a full equivalence between the ASYNNNI model and the one-dimensional Ising model, where the role of the nearest-neighbor interaction of the latter is played by the V 2 interaction in the former. We comment on the general applicability of low levels of the CVM approximation to systems equivalent to the one-dimensional Ising model.
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