【作者】 李柏茹；

【导师】 张凯锋；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2013， 博士

【摘要】 本文采用机械合金化与真空热压烧结相结合的技术制备了Nb-xW（x=10、20、30wt.%）、Nb-28.5W-5Cr、Nb-27W-10Cr和Nb-27W-10Si难熔合金，利用三因素三水平正交实验研究了Nb-W合金机械合金化过程中球磨时间，球料比和固液比等球磨参数对混合粉体质量的影响，制定了Nb-W、Nb-W-Cr和Nb-W-Si合金热压烧结工艺，采用烧结-锻造短流程工艺成形了Nb-W合金前缘模拟件，并对热压后的组织和室温力学性能进行了研究，探讨了Nb-W合金的高温氧化行为以及合金化元素Cr和Si对其氧化行为和室温力学性能的影响，考察了Nb-W合金高温压缩变形行为，并建立了Nb-W合金的热加工图。机械合金化研究结果表明，球磨粉末的颗粒尺寸主要由固液比控制，而杂质Fe含量则主要受球料比和球磨时间的影响，三个球磨参数综合作用着粉体的细化及形貌演变过程。球磨过程中，粉体发生了合金化，由粗粉的Nb（W）ss和W（Fe）ss逐步转变为细粉的Nb（W, Fe）ss和W（Fe）ss，最终转化成W（Nb, Fe）ss和Fe2Nb。综合考虑以上因素确定制备Nb-W复合粉体最优的球磨参数为：球磨时间为24h，球料比为10:1，固液比为1:0.2。分别在1800℃、1700℃、1600℃温度下，施加30MPa压力，保温90min制备了致密的Nb-W、Nb-W-Si和Nb-W-Cr合金，合金的组织分别为单相Nbss，Nbss+Wss+Nb₅Si₃+Nb₃Si和Nbss+NbCr₂。Nb-W合金的维氏硬度和弯曲强度随着W含量的增加逐渐增高，而室温断裂韧性先升高而后降低，综合考虑W含量对室温力学性能的影响，确定Nb-W合金中最佳W含量为30wt.%。在Nb-30W合金中分别添加Cr、Si元素后，合金的维氏硬度升高，而弯曲强度和室温断裂韧性降低，这是添加合金元素后合金中分别出现的硬脆NbCr₂和Nb₅Si₃、Nb₃Si导致的。采用烧结-锻造短流程工艺在1800℃条件下成形了Nb-30W合金前缘模拟件，零件成形质量好，内部组织致密，其室温力学性能与热压的Nb-30W合金相同。Nb-W合金在1000℃恒温氧化时， Nb-10W合金氧化膜从基体剥离，而Nb-20W和Nb-30W合金不同程度的出现了“粉化”氧化现象，均体现了较弱的抗氧化性能。1300℃恒温氧化结果表明，随着W含量的增加，Nb-W合金的氧化增重逐渐降低，抗氧化性能提高，但三个成分Nb-W合金氧化膜均与基体不同程度分离，不能作为抗氧化材料使用。在Nb-30W合金中分别添加10wt%的Cr、Si后，由于氧化膜中出现了CrNbO₄和SiO₂保护相，1000℃氧化时未出现“粉化”氧化现象，1300℃氧化时氧化膜致密且与基体结合良好，抗氧化性能得到改善；添加5wt.%Cr后，1000℃亦未出现“粉化”氧化，但其组织在1300℃时已由两相Nbss和NbCr₂转变成单相Nbss，抗氧性能下降。分别在1000℃、1300℃、1400℃、1500℃和1600℃进行Nb-W合金高温压缩变形，研究了其在不同应变速率0.001s-1，0.01s-1和0.1s-1下的变形行为，建立了热变形应力应变之间的关系，绘制了应变量为0.3的Nb-20W合金的高温压缩热加工图。结果显示，Nb-20W合金在1300～1550℃温度范围内，10^-3～10^-1s^-1应变速率下，热加工性良好。更多还原

【Abstract】 In the present research, Nb-xW（x=10,20,30wt.%）, Nb-28.5W-5Cr,Nb-27W-10Cr and Nb-27W-10Si refractory alloys were prepared by mechanicalalloying and uniaxial hot pressing, and a model of leading edge were fabricated bysinter-forging short process. The effects of ball-milling parameters on the qulity ofNb-W powders were quantitatively investigated using orthogonal test of threefactors at three levels. Meanwhile, the hot-pressed sintering processes of Nb-W,Nb-W-Cr and Nb-W-Si alloys were drawn up, the microstructure and mechanicalproperties at room temperature of hot pressed materials were studied. Moreover,the high temperature oxidation behaviors of Nb-W alloy and the effect of Cr and Sion the oxidation behaviors of Nb-W alloy have been studied. The high temperaturecompressive deformation behaviors of Nb-W alloys were investigated and theprocessing maps were drawn.Results of the mechanical alloying indicated that the particle size of milledpowders was mainly dominated by the solid-to-liquid ratio. The content ofimpurity Fe was mainly determined by the ball-to-powder ratio and the millingtime. The refining process and morphology evolution of the powder were affectedsynthetically by all three parameters. The results of mechanical alloying showNb（W）ss and W（Fe）ss phases in the coarse powders transformed to Nb（W, Fe）ssand W（Fe）ss, and eventually to the W（Nb, Fe）ss and Fe2Nb in the refined powders.According to the analysis above, the best paramters were choosed to be as follows,the milling time of24h, ball-to-powder ratio of10:1and solid-to-liquid ratio of1:0.2.Nb-W, Nb-W-Si and Nb-W-Cr alloys were hot pressed at1800℃,1700℃and1600℃for90min with pressure of30MPa, respectively. Microstructures ofthree alloys consist of single phase Nbss, Nbss+Wss+Nb₅Si₃+Nb₃Si andNbss+NbCr₂, respectively. The vicker hardness and flexural strength of Nb-Walloys increased and the room temperature fracture toughness decreased with theincreasing of W content. Based on mechanical test, Nb-W alloy with30wt.%Wobtained the best mechanical properties at room temperature. Additions of Cr andSi increased the vicker hardness and reduced the flexural strength and roomtemperature fracture toughness of Nb-30W alloys, which were caused by the hardand brittle NbCr₂in Nb-W-Cr, Nb₅Si₃and Nb₃Si in Nb-W-Si alloys, respectively.Moreover, a model of Nb-30W leading edge was successfully fabricated bysinter-forging short process at1800℃. The model displays a good surface qualityand high relative density. And the model contained the similar mechanical properties as well as the hot-pressed Nb-30W alloy.Nb-W alloys were exposed at1000℃, the scale on Nb-10W alloy spalledfrom the base metal and the―pest‖phenomenon appeared the scales on Nb-20Wand Nb-30W alloys. The results at1000℃indicating the poor oxidation resistance.In addition, the results of isothermal oxidation at1300℃indicated that the masschange of Nb-W alloys reduced, the oxidation resistance was improved withincreasing of W contents. The scales of three Nb-W alloys spalled from the basemetal show the poor oxidation resistance. However, the additions of10wt%Cr and10wt%Si into Nb-30W alloy result in the formation of the protective phaseCrNbO₄and SiO₂. The―pest‖phenomenon disappeared at1000℃. The relativedense scales combined well with the alloy’s matrix at1300℃. The results aboveindicate that addition of10wt%Cr and10wt%Si into Nb-30W alloy provide thegood oxidation resistance. Meanwhile, after5wt%Cr was added into Nb-30Walloy, the―pest‖phenomenon also disappeared at1000℃and showed the goodoxidation resistance. But the oxidation resistance still descreased since two phasesNbss+NbCr₂were transformed to single phase Nbss at1300℃.Nb-W alloys were compressed at1000℃,1300℃,1400℃,1500℃and1600℃, respectively. The deformation behaviors were studied in the differentstrain rates of0.001s-1,0.01s-1and0.1s-1. Meanwhile, the stress-strain relations ofhot deformation were established. The processing maps （=0.3） of hot compressingof Nb-20W alloy were drawn. The results show the good hot workability in therange of1300～1550℃at the strain rate of10^-3～10^-1s^-1 for Nb-20W alloy.更多还原