Phase Equilibria in the TiO2-Rich Part of the TiO2-CaO-SiO2-10 Wt Pct Al2O3-5 Wt Pct MgO System at 1773 K

Metallurgical and Materials Transactions B - The phase equilibria of the TiO2-CaO-SiO2-10 wt pct Al2O3-5 wt pct MgO system in the TiO2-rich part were...     

Ti-5A1-2Mo-3Zr合金的低温形变

对Ti-523合金由室温到-75℃之间的拉伸性能和形变行为作了系统研究,发现淬火态在-75℃拉伸仍保持高塑性,而经回火的试样则塑性较低。两者的强度在低温下均升高,可比室温强度高10%。形变机理则由室温的滑移为主变为低温下的以孪生为主,交替温度可能在-15℃~-30℃之间。低温形变出现一种双重\     

A Coupled Small and Wide-Angle X-Ray Scattering Study of Phase Transformation Mechanisms in U-6Wt Pct Nb

Metallurgical and Materials Transactions A - The elevated temperature phase transformation kinetics of U-6wt pct Nb in both wrought and cast conditions were investigated using in-situ...     

Fe3Al合金的冲击韧性

研究了不同温度下Fe3Al基合金冲击韧性的变化规律，确定了冲击载荷下该合金的韧－脆转化温度，考察了冲击载荷下该合金的断裂方式，晶粒组织和位错运动的变化情况。     

Fe3Al金属间化合物多孔材料的研究

采用粉末冶金方法制备了Fe3Al多孔材料，研究了烧结温度等工艺参数对Fe3Al多孔材料的力学性能、过滤特性的影响，考察了，制得的Fe3Al多孔材料的高温强度和耐腐蚀性能。结果表明，Fe3Al烧结多孔材料具有很好的抗拉强度、渗透特性和耐腐蚀性能。     

温度与镀层对Sn-0.7Cu焊料合金润湿性的影响

主要研究了真空状态下,焊接温度为530,560和590 K时,Sn-0.7Cu焊料合金在镀Cu、镀Ni、镀Ni/Ag和镀Ni/Au基板上的润湿性.结果表明:提高钎焊时的焊接温度,有助于降低液态Sn-0.7Cu焊料合金的表面张力,从而增大Sn-0.7Cu焊料合金在焊接基板上的润湿性.在相同的焊接条件下,Sn-0.7Cu焊料合金在镀Ni/Ag和镀Ni/Au基板上的润湿性比其在Cu和镀Ni基板上的润湿性好.     

An induction heating process with coil design and solutions avoiding coarsening phenomena of Al-6 Pct Si-3 Pct Cu-0.3 Pct Mg alloy for thixoforming

During the thixoforming process, it is very important to obtain a uniform temperature, which affects the uniformity of the solid fraction, throughout the billet. Consequently, a heating method that can provide a suitable temperature profile throughout the billet must be chosen. Other parameters that must be considered include heating time (in order to minimize the total processing time), the level of control, and temperature consistency. An optimal design of the induction coil has been identified that best meets these criteria. In a previous study, the theoretical optimal coil design was verified through the FEM simulation of the induction heating process by using a general purpose finite element analysis code, ANSYS. So, in this study, the suitability of the coil design was also demonstrated by conducting induction-heating experiments. The optimal reheating conditions to apply the thixoforming (thixoforging and semisolid die casting) process were investigated by varying the reheating time, the holding time, the reheating temperatures, the capacity of the induction heating system, and the size of the adiabatic material. The final holding time was observed to be the most important factor in obtaining a fine globular microstructure and to prevent coarsening in the three-step reheating process.     

Effect of Impurity Content on Cavitation in the Superplastic Zn-22 Pct Al Alloy

Micrograin superplasticity refers to the ability of some materials to exhibit neck-free strains of several hundred percent upon deformation. The two basic prerequisites for the observation of micrograin superplasticity are (a) a temperature greater than about one half of the melting point,T _m, and (b) a fine, stable, and equiaxed grain size that does not undergo significant growth during elevatedtemperature deformation. In addition to these two prerequisites, grain boundaries need to be mobile, high-angled, and able to resist tensile separation.     

Ti-22Al-25Nb合金板条组织高温高周疲劳行为

研究了双尺寸板条组织的Ti-22Al-25Nb合金在650 ℃和700 ℃下的高周疲劳行为,采用升降法测试了合金的高温高周疲劳强度极限,当应力比R=-1,循环周次Nf=107次时,650 ℃和700 ℃的疲劳强度极限分别为470 MPa和400 MPa。对于双板条组织的Ti-22Al-25Nb合金,其疲劳裂纹既可萌生于试样表面,也可萌生于次表面,并且高周疲劳裂纹在次表面形核的试样具有更高的疲劳寿命。此外,研究发现双尺寸板条组织在高温高周疲劳损伤过程中以胞状析出的形式发生B2→β+O相变,形成组织中的不均匀区域,促使疲劳裂纹在此优先形核。     

Effect of Fe on ductility and cavitation in the superplastic Zn-22 Pct Al eutectoid

In this investigation, the ductility and cavitation behavior of five grades of the superplastic Zn-22 pct Al were studied under identical conditions of grain size, temperature, and initial strain rate. These five grades were prepared from high-purity Al and Zn using the same procedure but different Fe impurity levels; grades A, B, C, D, and E contain 1, 40, 120, 400, and 1460 ppm of Fe, respectively. A comparison between the present results and those reported earlier for the creep behavior of the five grades of Zn 22 pct Al demonstrates that while the presence of Fe has no noticeable effect on the steady-state creep rates during deformation in the superplastic region (where maximum ductility occurs), it has a pronounced effect on the ductility and fracture behavior of the alloy. The experimental data show that there is a significant drop in the average elongation to fracture when Fe concentration exceeds 125 ppm, and that the ductility of grade E is approximately 50 pct of grade A for initial strain rates less than 10⁻² s⁻¹. In addition, the data reveal two important findings regarding cavitation behavior. First, neither the initial grain size nor the occurrence of grain growth has an effect on cavitation that is as significant as that arising from the presence of excessive impurities. Second, the presence of other impurities in addition to Fe in Zn-22 pct Al has the effect of enhancing cavitation. The effect of Fe, alone or in the presence of other impurities, on ductility and cavitation in Zn 22 pct Al is examined in terms of phenomena associated with impurity segregation at boundaries. Formerly Research Associate, Materials Section, Department of Mechanical and Aerospace Engineering, University of California, Irvine, CA Formerly Graduate Research Assistant, Materials Science & Engineering, Department of Chemical and Biochemical Engineering, University of California, Irvine, CA This article is based on a presentation made at the “High Temperature Fracture Mechanisms in Advanced Materials” symposium, as a part of the 1994 Fall meeting of TMS, October 2-6, 1994, in Rosemont, Illinois, under the auspices of the ASM/SMD Flow and Fracture Committee.     

退火温度对Ti-3Al-4.5V-5Mo钛合金显微组织和织构的影响

研究了退火温度对Ti-3Al-4.5V-5Mo钛合金丝材显微组织和织构的影响. 结果表明, 随着退火温度的提高, 初生α相的形态逐渐由条状α和球状α的混合组织向球状组织过渡, 晶粒尺寸逐渐增加. 当退火温度达到880 ℃时, 转变成粗晶片状组织. 两相区退火时,α相出现(φ1,～0°,φ2)织构组分, 其强度随着退火温度的升高而略有增加,β相(φ1,～0°,φ2)织构组分随着退火温度的升高逐渐增强. Β区退火后织构依然明显,α和β相织构分别主要为(φ1,～0°,φ2)和(φ1,～45°,0°).两相区退火加热时,α和β相发生了原位再结晶和形核长大再结晶, 在随后的炉冷过程中, β相向α相的转变主要是以在原有α相颗粒上的长大机制进行.     

Investigation on Cracking in Surfacing Layer of Ni_3Al Base Alloy

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Effect of Cryogenic Thermal Cycling on Tribocorrosion Performance of Fe-Based Bulk Amorphous Alloy in 3.5 Pct NaCl Solution

Metallurgical and Materials Transactions A - The effects of cryogenic thermal cycling on the tribocorrosion behavior of Fe41Co7Cr15Mo14C15B6Y2 bulk amorphous alloy were studied in 3.5 pct...     

High Strain Rate Compression of Martensitic NiTi Shape Memory Alloy at Different Temperatures

The compressive response of martensitic NiTi shape memory alloy (SMA) rods has been investigated using a modified Kolsky compression bar at various strain rates (400, 800, and 1200 s^?1) and temperatures [room temperature and 373 K (100 °C)], i.e., in the martensitic state and in the austenitic state. SEM, DSC, and XRD were performed on NiTi SMA rod samples after high strain rate compression in order to reveal the influence of strain rate and temperature on the microstructural evolution, phase transformation, and crystal structure. It is found that at room temperature, the critical stress increases slightly as strain rate increases, whereas the strain-hardening rate decreases. However, the critical stress under high strain rate compression at 373 K (100 °C) increase first and then decrease due to competing strain hardening and thermal softening effects. After high rate compression, the microstructure of both martensitic and austenitic NiTi SMAs changes as a function of increasing strain rate, while the phase transformation after deformation is independent of the strain rate at room temperature and 373 K (100 °C). The preferred crystal plane of the martensitic NiTi SMA changes from (\( 1\bar{1}1 \))_M before compression to (111)_M after compression, while the preferred plane remains the same for austenitic NiTi SMA before and after compression. Additionally, dynamic recovery and recrystallization are also observed to occur after deformation of the austenitic NiTi SMA at 373 K (100 °C). The findings presented here extend the basic understanding of the deformation behavior of NiTi SMAs and its relation to microstructure, phase transformation, and crystal structure, especially at high strain rates.     

高性能Mg-6Sn-3Al-1Zn合金的制备工艺研究

通过改善铸态镁合金制备工艺,得到一种组织均匀、性能优异的Mg-6Sn-3Al-1Zn合金,合金抗拉强度、屈服强度、延伸率分别达到219MPa、82MPa、16%,晶粒尺寸为133.35μm。     

Ti-10V-2Fe-3Al合金热工艺的研究

利用Gleeble-1500热模拟试验机以压缩变形方式研究了Ti-10V-2Fe-3A1合金热变形行为，并研究了经不同变形参数变形后两种热处理制度下微观组织的变化。研究结果表明，合金在B相变点以上或以下的变形时，变形速率和变形温度对合金的流变应力影响不同。在相变点以下变形时，相同应变下变形温度的选择并没有明显影响合金最终的微观组织，合金在变形过程中没有发生动态再结晶。具相同应变时，较高的应变速率比较低的应变速率更容易破碎合金中的初生α相。经过变形和热处理后，同一温度变形的合金在低应变速率下变形时比较高应变速率有较大的晶粒(相变点及以上)和较长的α相(相变点以下)。