Materials Characterization最新文献

In order to explore whether (Nb,W) co-alloying TiAl-based alloys with relatively higher W addition have better high-temperature tensile rupture property, Ti-44Al-4Nb-1 W-0.1B alloy is designed and prepared. Ti-44Al-8Nb-0.1B alloy and Ti-44Al-7.2Nb-0.2 W-0.1B alloy are also prepared for comparative study. The rupture property testing is carried out at 800 °C and different tensile stresses. The property data, macro/microstructure evolution, fracture surface, W content, crack failure behaviors are studied. The results show that the (Nb,W) co-alloying alloys have better rupture property than the pure Nb alloying alloy. For the (Nb,W) co-alloying alloys, the higher W contained Ti-44Al-4Nb-1 W-0.1B alloy has the better property under lower tensile stress, and the lower W contained Ti-44Al-7.2Nb-0.2 W-0.1B alloy has the better property under higher tensile stress. The relationships of rupture life $t$ and stress $\sigma$ for the three alloys are given. All the three alloys have a coupling fracture mode of ductile fracture and brittle fracture. The ductile fracture exhibits the typical dimple characteristics. The brittle fracture exhibits the typical trans-granular cleavage, river-like pattern and trans-lamella fracture characteristics. The higher the stress, the more brittle fracture characteristics there are. After rupture property testing, the (α₂ + γ) lamella colony sizes of the three alloys all decrease, indicating that DRX and grain boundary slip occur not only along (α₂ + γ) lamella colony boundary, but also inside it. The colony boundary regions have the stress concentration, where the B2 phase produces the better buffering and coordination, and as well as the dislocation tangles, DRX and grain boundary slip can be found by EBSD and TEM. EPMA results show that the more W added in the alloy, the more W content is in the (α₂ + γ) lamella matrix, which is beneficial for the rupture property. However, more W addition will also lead to the formation of more B2 phase in the initial as-cast microstructure. So that, under higher tensile stress, when the stress intensity factor K is higher, the crack failure is more likely to occur.

In this work, the resistance against nanoindentation of the Laser Powder Bed Fusion (LPBF) CuCrZr alloy specimen was studied at the ramp load of 2000–3000 μN on 100 points. It was found that the triangular shape indentation cavity and the pile-up material increased along the diagonal direction. The LPBF CuCrZr alloy contained few partly melted LPBF particles which have three different structures namely columnar, cellular and equiaxed. The nanowear test was conducted on the above three structures. The tribological property of partly melted LPBF particles was analyzed at 2000 μN cyclic load. The wear depth in the partly melted LPBF particles at the columnar structure for cycle-1, cycle-2 and cycle-3 were 836 nm, 918 nm and 980 nm, respectively. The wear depth in the partly melted LPBF particles at the cellular structure for cycle-1, cycle-2 and cycle-3 were 650 nm, 780 nm and 810 nm, respectively. The wear depth in the partly melted LPBF particles at the equiaxed structure for cycle-1, cycle-2 and cycle-3 were 650 nm, 720 nm and 780 nm, respectively. The obtained outcomes were correlated with the tribological behavior of non-defective part. The non-defective part exhibited higher wear resistance than the partly melted LPBF particles. The percentage increase in wear resistance at the columnar non-defective part over partly melted LPBF particles for cycle-1, cycle-2 and cycle-3 were 22.24 %, 20.5 % and 20.4 %, respectively. Similarly, the cellular and equiaxed non-defective parts have higher wear resistance when compared to the partly melted LPBF particles. Moreover, the decrease in Coefficient of friction was observed from one cycle to the next cycle both in the partly melted LPBF particles and non-defective part in all three structures.

In this work, the microstructure characteristics of Al-Mg-Si-Cu alloy were investigated under various hot deformation Zener-Hollomon parameters. Intergranular and electrochemical corrosion behaviors of solid solution-aged samples with lnZ values of 19.3 to 31.5 were analyzed. The results indicated that the corrosion resistance of the samples initially increased and then decreased as the lnZ value decreased. Precipitates and continuous Cu-rich films on high angle grain boundaries are the primary causes of their susceptibility to corrosion. Conversely, the absence of continuous effective cathodes on low angle grain boundaries is conducive to impeding intergranular corrosion. The Z23 sample (lnZ = 23.1) showed the highest corrosion properties due to its relatively low recrystallization volume fraction of 28.2 % and a higher proportion of low angle grain boundaries in the microstructure. It is promising to enhance the corrosion properties of alloys without compromising mechanical properties by controlling hot deformation parameters.

In current work, the effect of nanoparticle size in Cu-Y₂O₃ alloy on the microstructure response after He/D sequential irradiation is studied using a transmission electron microscope (TEM) and nanoindentation. The results indicated that the direct contribution of nanoparticle/matrix interface to defect evolution and irradiation hardening of ODS Cu is limited when the nanoparticle size is larger than 20 nm. The difference in the proportion of ∑3 grain boundary and small angle grain boundaries was observed with different nanoparticle sizes, which suggests that the indirect effects on the sink strength caused by changes in the nature of grain boundary cannot be ignored, especially for the large particles. Besides, the distribution of bubbles after sequential He/D irradiation was highly similar to that in single He irradiation.

Interstitial hydrogen atoms in titanium usually deteriorate the mechanical properties of titanium by brittle hydride phase or hydrogen-enhanced localized plasticity. In this study, hydride was used as the second phase to improve the tensile strength and elongation of TA1 pure titanium. The continuous coarse hydride network is precipitated in TA1 pure titanium after the hydrogen-charged. Then pulse current treatment is used to decompose the original coarse hydride network and reduce the size and number of hydride strips. Finally, a small uniform hydride network is formed in TA1 pure titanium. The results of tensile experiments indicate that the tensile strength of hydrogen-charged TA1 pure titanium treated by pulse current increases from the 286.4 MPa to 316.1 MPa and the elongation increases from the 47.6 % to 56.8 %. The improvement of mechanical properties demonstrate that the small and uniform hydrides can significantly improve the mechanical properties of TA1 pure titanium. In hydrogen-charged TA1 pure titanium treated by pulse current, the increment of strength is mainly caused by hard phase hydrides, and the increase in plasticity is attributed to the role of twins in coordinating deformation during plastic deformation. This study manifests that in addition to being used as a temporary alloying element to optimize the microstructure of titanium, hydrogen can also be directly act as a second phase in titanium to improve the mechanical properties.

The structural characterization of two-metal phase systems at nanometer scale which present partial or total mixing, is extremely challenging. In the present work, a model to reproduce the x-ray diffraction patterns of multilayers composed by two miscible metals, Mo and W, is presented. Two different deposition conditions were used to obtain different stress states (compressive and tensile). From the proposed model, the contribution of each metal phase was discerned, the intra layer disorder and the level of mixing at the interface were quantified. The comparison between structures deposited sequentially, with others obtained by co-evaporation is also carried out to better understand the details of the interdiffusion and to separate them from the effects of roughness and elastic adaptation stresses. Microstructure characterization by scanning and transmission electron microscopy was compared and discussed with the diffraction analysis.

The effect of twinning and de-twinning on precipitation behavior of a rolled AZ80 alloy has been examined. Results showed that both twinning and de-twinning deformation can promote the precipitation of continuous precipitates. And only dense continuous precipitates can be formed inside twinned and de-twinned regions. The high density crystal defects existing in the twinned and de-twinned regions increase the diffusion rate of solute elements and provide more nucleation sites for precipitation, resulting in a homogeneous and dense distribution of continuous precipitates in these regions. Comparing to direct aging, both post-twinning aging and post-de-twinning aging can remarkably increase the yield strength and peak strength by promoting the precipitation of continuous precipitates. For tension and compression, both direct aging and post-de-twinning aging reduce the strain corresponding to peak strength (ε_p) and static toughness (U_T) to a close level. In contrast, post-twinning aging exhibits little loss in ε_p and largely increases U_T. The strengthening and toughening mechanisms were also discussed in detail.

Grain size has a significant impact on the properties of materials, and is crucial for predicting material properties. Traditional grain size measurement relies heavily on human operators, leading to subjective results, and existing machine learning methods are typically material-specific, requiring significant labeling and training efforts for each new material. This paper provides insight into developing a deep learning-based generic grain boundary detection model (GeGra) from different material micrographs. The model is trained on 1006 images from various microscopy techniques such as light optical, Kerr, and scanning electron microscopy, acquired at different magnifications for different materials such as copper, austenite, brass, sintered hard magnet, hard metal, bronze, nickel silver, and aluminum. The developed GeGra model effectively handles visual artifacts and substructures such as twin grains, which often pose challenges for material-specific, state-of-the-art grain boundary segmentation models. The developed model achieved an IoU score of 69 % on a diverse test set and enables accurate grain size analysis using external image analysis software in less than one minute, according to ASTM standards, which is more than 5 times faster than the manual method. The developed model prioritizes generality with objective that it can have broader applicability for various materials instead of high-precision grain boundary detection. Additionally, the model has the potential to be a foundational tool for generalized grain size analysis in material microscopy, reducing the effort required for such analysis and assisting both material science experts and machine learning users.