钨粉粒度和烧结温度对添加La_2O_3的钨合金性能和组织的影响

通过传统粉末冶金的方法制备了添加0.15%La_2O_3的92W合金,研究了粗细两种不同粒度钨粉在1 490～1 520℃烧结温度下对制备的高密度92W合金的力学性能和显微组织的影响。结果表明:随着烧结温度的升高,细钨粉制备的合金抗拉强度下降,延伸率增加,冲击韧性先增加后下降;粗钨粉制备的合金抗拉强度先增加后下降,延伸率和冲击韧性增加。因此,采用不同粒度钨粉制备的含La_2O_3钨合金要获得最佳的综合力学性能应当采用不同的烧结温度。La_2O_3颗粒在合金组织中存在聚集和偏析,且随着烧结温度的不断升高越来越显著。细钨粉制备的钨合金在较低温度下烧结时,得到的钨晶粒度较粗钨粉制备的合金更粗大,而烧结过程采用较高温度时,得到的结果却相反。     

烧结温度对SPS制备TA15钛合金组织与拉伸性能的影响

利用放电等离子烧结法(SPS)制备TA15钛合金试样，并采用扫描电子显微镜、自动转塔显微硬度计和电子万能试验机研究烧结温度对合金显微组织、硬度与力学性能的影响。结果表明，烧结温度对TA15钛合金微观组织具有显著影响，当烧结温度在900℃以上时，TA15钛合金由等轴组织转变为魏氏组织，且原始β相尺寸增大，魏氏组织中片层间距更加细密。在烧结温度850℃、烧结时间5 min、烧结压力40 MPa条件下，TA15钛合金具有最佳的力学性能，室温抗拉强度和屈服强度分别为1032.15、943.39 MPa,延伸率为17.72%。     

原料粒径与烧结温度对放电等离子烧结Ti-29Nb-13Ta-4.6Zr合金组织和性能的影响

利用放电等离子烧结技术(SPS)制备生物医用Ti-29Nb-13Ta-4.6Zr合金,研究原料粒径与烧结温度对合金显微组织和力学性能的综合影响。结果表明:烧结合金组织由β-Ti相基体及少量未熔化金属颗粒和残留α-Ti相组成,烧结温度的升高会减少未熔化金属颗粒和残留α-Ti相;在相同烧结温度下,Nb、Ta、Zr金属颗粒粒径的减小,会促使烧结合金中的β-Ti相组织更为均匀并使未熔化金属颗粒明显减少,从而降低合金的压缩弹性模量和提高合金的抗压强度与致密度;在Nb、Ta、Zr金属颗粒粒径为10.5μm和烧结温度为1 200℃时,合金获得了压缩弹性模量为46 GPa、抗压强度为1 550 MPa的最佳综合力学性能。     

镍的添加方式对钨基高比重合金显微组织和性能的影响

对镍加入到钨基高比重合金中的四种方式进行了研究。结果表明，镍以共还原法的方式加入，所得合金在液相烧结时的活化作用下，降低了合金的烧结温度，钨晶粒微细，防止了脆性相WNi4，金属间化合物的形成，同时合金具有较高的物理和力学性能。     

二步烧结法对钨基高密度合金组织及性能的影响

采用直接液相烧结法和二步烧结法(固相烧结+液相烧结)制备了93W-4.55Ni-1.95Fe-0.5Co钨基高密度合金,研究了其性能和显微组织。结果表明,二步烧结法可以控制合金的烧结变形,且有利于钨颗粒与粘结相的均匀分布,合金的力学性能尤其是塑韧性大大提高。     

高比重W—Ni—Fe合金的变形强化

在三个钨含量的Ｗ－Ｎｉ－Ｆｅ合金变形强化过程中，研究了变形量和力学性能与显微组织之间的关系。试验结果表明：随着钨合金变形量的增加，变形合金的强度和硬度亦增加，当变形量超过１５％后，高钨含量合金的变形强化作用逐渐减小。在变形合金的显微组织中，钨颗粒沿棒料轴向明显拉长，同时解理断裂成为断口的主要形式，并显现出钨合金断面上的滑移带。本文还讨论了变形合金在真空下，最佳调质退火温度和两相钨合金的形变特点、变     

高碳铌钨合金HCNb521的生产工艺研究

对高碳铌钨合金HCNb521烧结条进行二次电子束熔炼,以控制合金的碳、锆及气体含量。分析了熔炼锭高温退火处理后的显微组织,并对比了高碳铌钨合金HCNb521及普通铌钨合金Nb521板材的力学性能。研究结果表明,碳含量的增加使铌钨合金中形成较多的第二强化相,提高了铌钨合金的强度;电子束熔炼可有效地控制铌钨合金锭坯的成分含量;高碳铌钨合金的材料力学性能较普通铌钨合金稍有提高。     

纳米晶钨合金粉末常压烧结的致密化和晶粒长大

高比重合金由于具有密度和强度高、延性好等一系列优异的性能,在军工上被用作动能穿甲弹材料.纳米材料被认为是21世纪应用前景最为广阔的新型材料.采用纳米粉末可望大大细化钨合金晶粒,显著提高合金的强度、延性和硬度等力学性能,因而是制备新型高强韧、高比重钨合金的一个很重要的研究方向.作者采用机械合金化(MA)工艺制备了纳米晶钨合金复合粉末,研究了纳米晶钨合金粉末在常压氢气气氛中的烧结致密化和在烧结过程中的钨晶粒长大行为.研究结果表明,MA纳米晶粉末促进了致密化,使致密化温度降低约100～200℃.在一般固相烧结温度时可以得到晶粒尺寸为3～5μm的细晶高强度合金.同时,指出了在液相烧结时存在的问题,即钨晶粒加速重排、产生晶粒聚集与合并,迅速发生钨晶粒长大,在较短时间内液相烧结时,钨晶粒尺寸又长大到接近传统高比重合金水平.     

退火温度对轧制态钨合金组织及性能的影响

本文对变形态95WNiFe合金进行了退火试验研究,退火温度分别为800℃、1000℃、1200℃和1450℃.通过对显微组织、抗拉强度和伸长率的分析测试,对比了不同退火温度对合金组织及性能的影响.结果表明:在1200℃时,钨颗粒开始出现再结晶现象,合金的抗拉强度由轧制态的1215 MPa降低到1050 MPa,伸长率由3％升高到8％;当温度达到1450℃时,显微组织形貌与烧结态相似,合金的抗拉强度和伸长率已经接近烧结态的水平;通过不同温度退火试验研究,确定了轧制态合金的最佳退火温度为800～1100℃.     

低氧MHC合金板材的制备及力学性能

采用粉末冶金方法和热轧工艺制备了低氧MHC合金轧制板材,通过化学分析、金相分析、硬度测试、拉伸力学性能测试研究了低氧MHC合金的显微组织和力学性能。研究表明：通过调节C/Hf原子比、钼粉还原并结合真空烧结等手段,可以有效降低合金中的氧含量。不同温度下退火后样品显微组织分析和力学性能测试结果对比表明,合金板材在1 300℃以下为回复阶段,随着退火温度的增加,1 300℃开始发生再结晶,强度和硬度逐渐下降,塑性提高,在1 600℃时再结晶完成,完全再结晶的低氧MHC合金板材塑性优异。     

Sintering of nano- and ultradispersed mechanically activated W-Ni-Fe powders and the manufacture of ultrahigh-strength heavy tungsten alloys

The structure and mechanical properties of nano- and ultradispersed mechanically activated heavy W-Ni-Fe and W-Ni-Fe-Co tungsten alloys (VNZh and VNZhK alloys, respectively) are studied. Mechanically activated nano- and ultradispersed charge powders are sintered by free sintering (thermally activated) and spark plasma sintering. The dependence of the density of the alloys made of the mechanically activated powders on the sintering temperature is found to have a nonmonotonic character with a maximum corresponding to the optimum sintering temperature. It is shown that an increase in the mechanical activation time and the acceleration of the milling bodies during mechanical activation lead to a decrease in the alloy particle size and the formation of nonequilibrium solid solutions and are accompanied by a decrease in the optimum sintering temperature of heavy tungsten alloys. Ultrahigh-strength tungsten alloys the mechanical properties of which are substantially higher than those of standard coarse-grained analogs are fabricated due to the optimization of the conditions of ball milling and high-rate spark plasma sintering of W-Ni-Fe powders.     

Effect of size and shape of tungsten particles on dynamic torsional properties in tungsten heavy alloys

The effect of the size and shape of tungsten particles on dynamic torsional properties in tungsten heavy alloys was investigated. Dynamic torsional tests were conducted on seven tungsten alloy specimens, four of which were fabricated by repeated sintering, using a torsional Kolsky bar, and then the test results were compared via microstructure, mechanical properties, adiabatic shear banding, and deformation and fracture mode. The size of tungsten particles and their hardness were increased as sintering temperature and time were increased, thereby deteriorating fracture toughness. The dynamic torsional test results indicated that in the specimens whose tungsten particles were coarse and irregularly shaped, cleavage fracture occurred predominantly with little shear deformation, whereas shear deformation was concentrated into the center of the gage section in the conventionally fabricated specimens. The deformation and fracture behavior of the specimens having coarse tungsten particles correlated well with the observation of the in situ fracture test results, i.e., cleavage crack initiation and propagation. These findings suggested that there would be an appropriate tungsten particle size because the cleavage fracture mode would be beneficial for the “self-sharpening” of the tungsten heavy alloys.     

Effect of cobalt addition on microstructure and mechanical properties of tungsten heavy alloys

The present investigation attempts to study the microstructure and mechanical behaviour of tungsten heavy alloys with different cobalt content. Alloys with 2 and 3% cobalt were synthesized using liquid phase sintering technique. The alloys were then vacuum heat treated and finally swaged. Quantitative microstructural analyses were undertaken by determining tungsten grain size, contiguity of tungsten and volume fraction of the matrix etc. Tensile results showed that the alloy with 3% cobalt exhibited inferior properties as compared to 2% cobalt alloy. Detailed microstructural and fractographic analysis were undertaken in order to understand these trends. Work hardening analysis showed the double slope behaviour of the alloys, which could be attributed to change in deformation behaviour from single phase matrix to two phase aggregate. It was also concluded that higher cobalt alloys needed further optimization in terms of thermo-mechanical treatment in order to realize their full potential in terms of mechanical properties.     

注射成形高比重合金的致密化与变形控制

研究了注射成形高比重合金的致密化和变形行为,实验表明在液相烧结过程中,由于重力的作用导致粘性流动,样品发生变形,对W含量较高的合金,采用2步烧结工艺可以有效地控制变形,在此工艺中,压坯首先在粘结相熔点温度以下烧结,形成W连通骨架,然后在高于粘结相熔点以上的温度下烧结较短时间以达到全致密,对于W含量较低的高比重合金,将原始混合粉末采用机械合金化,然后再进行固相烧结,可以得到性能很好的无变形合金。     

钨基重合金的注射成形工艺

研究了3种钨基重合金的金属注射成形工艺(MIM),重点研究了脱脂和烧结两个工序,分析了烧结温度对机械性能、断口和显微组织的影响,列举了烧结收缩、机械性能和最佳烧结温度等数据。     

细晶钨合金内部组织均匀性研究

喷雾干燥法制备超细粉末,使用低温烧结技术制备钨合金制品,分别对超细钨合金和常规钨合金进行力学性能测试,并采用超声波探伤技术检测超细钨合金和常规钨合金的内部组织,探伤结果显示超细晶钨合金内部没有发现缺陷,而常规钨合金内部有两处鸟巢状缺陷,分别对缺陷部位和没有缺陷部位进行金相分析,金相显示缺陷部位是液相缺失导致的钨颗粒聚集,聚集的钨颗粒没有液相填充出现很多孔洞。     

钨基重合金注射成形工艺研究

研究了三种钨基重合金的金属注射成形工艺（MIM）,重点研究了脱脂和烧结两个工序,分析了烧结温度对力学性能、断口和显微组织的影响。列举了烧结收缩、力学性能和最佳烧结温度等数据。     

Sintering atmosphere effects on tensile properties of heavy alloys

The sintering atmosphere has a direct bearing on the residual porosity which in turn has a strong negative influence on the tensile properties of W-Ni-Fe heavy alloys. The present investigation uses various sintering atmospheres to understand pore formation, densification, microstructure, and tensile properties of heavy alloys with tungsten contents ranging from 88 to 97 wt Pct. Pore formation when sintering in a dry hydrogen atmosphere is linked to water vapor generation and its entrapment in pores. A hydrogen dew point effect is associated with solution-reprecipitation of tungsten during liquid phase sintering. The beneficial effect of vacuum sintering has been analyzed in terms of removal of the gases before pore closure. Property degradation during long time vacuum sintering is attributed to preferential matrix vaporization. The negative effect of long sintering times in dry hydrogen is attributed to pore coarsening, which is removed by a three-stage sintering atmosphere treatment.     

固相烧结低钨含量W-Ni-Fe合金的微观结构与力学性能

采用固相烧结工艺(1 300℃保温1 h)制备低钨含量(质量分数为60%~80%)的W-Ni-Fe合金,测定合金的抗拉强度、抗压强度和伸长率,利用金相显微镜观察合金的显微组织,并通过扫描电镜(SEM)观察合金断口形貌,研究钨含量对固相烧结W-Ni-Fe合金力学性能与微观结构的影响。结果表明:随钨含量降低,合金的孔隙率和平均孔径减小,抗拉强度增大,伸长率显著提高,抗压强度变化不大。W含量为60%~80%的W-Ni-Fe合金,其孔隙率为17.8%~21.4%,抗拉强度为231~262 MPa,抗压强度2 450~2 550 MPa,伸长率为0.3%~2.3%,压拉比为9.45~11.04,都能满足易碎型穿甲弹弹芯材料的性能要求。     

几种变形方式对钨合金组织性能及绝热剪切敏感性的影响

讨论了变形方式、变形量、变形材料的受力状态及微观组织结构等方面因素对材料性能和绝热剪切敏感性的影响。钨合金的受力状态、颗粒形状、微观组织取向对材料的变形、破坏和变形局域化机制有重要影响。X射线分析表明，旋锻后的钨合金组织有织构存在。力学性能的各向异性导致了材料绝热剪切破坏难易程度上的差异。