机械合金化与放电等离子烧结制备Ti-45Al-5.5(Cr,Nb,B,Ta)合金

Preparation of Ti-45Al-5.5(Cr,Nb,B,Ta) alloy by mechanical milling and spark plasma sintering

采用双步球磨法和放电等离子烧结技术制备细晶Ti-45Al-5.5(Cr,Nb,B,Ta)(摩尔分数,%)合金,利用扫描电子显微镜(SEM)和X射线衍射仪(XRD)等对球磨后的粉末形貌、相组成以及烧结块体的显微组织结构进行观察和分析,研究烧结温度对Ti-45Al-5.5(Cr,Nb,B,Ta)合金显微组织和力学性能的影响。结果表明:双步球磨粉末的颗粒形状较规则,其颗粒尺寸为10～40μm,内部结构较均匀,主要由TiAl和Ti_3Al相组成;放电等离子烧结后的块体主要由主相TiAl、少量的Ti_3Al相及Ti_2Al和TiB_2相组成;当烧结温度为1000℃时,烧结块体主要为等轴晶组织,等轴晶粒平均尺小于500 nm;当烧结温度为1100℃时,烧结块体致密、无孔洞,部分等轴晶粒明显长大;随着烧结温度的升高,Ti-45Al-5.5(Cr,Nb,B,Ta)合金的显微硬度随之增大,抗压强度和抗弯强度却随之降低;压缩断口形貌分析表明:Ti-45Al-5.5(C r,Nb,B,Ta)合金在1000℃时,属于沿晶断裂,在1100℃时,断口以沿晶断裂为主,存在部分解理断裂。弯曲断口形貌分析表明:Ti-45Al-5.5(C r,Nb,B,Ta)合金以沿晶断裂为主,存在部分解理断裂。

A fine-gained TiAl alloy with composition of Ti-45Al-5.5（Cr, Nb, B, Ta）（mole fraction, %） was prepared by double mechanical milling （DMM） and spark plasma sintering （SPS）. The effects of sintering temperature on the microstructure and mechanical properties of the Ti-45Al-5.5（Cr, Nb, B, Ta） were studied by X-ray diffractometry（XRD）, scanning electron microscopy （SEM） and mechanical testing machine. The results show that the morphology of double mechanical milling powder is regular with sizes of 10-40 μm and the internal structure is even. TiAI and Ti3Al are the main phases in the powders, with few phases such as Ti3Al, Ti2Al and TiB2 observed in the SPS bulk samples of Ti-45Al-5.5（Cr, Nb, B, Ta） alloy. For samples sintered at 1 000 ℃, the microstructure of equiaxed crystal grain with sizes less than 500 nm is achieved. For samples sintered at 1 100 ℃, the sizes of few equiaxcd crystal grain obviously increases. The SPS bulk samples exhibit better microstructures. The micro-hardness of the SPS bulk samples at 1 000 ℃ is obviously lower than that oftbe SPS bulk samples at 1 100 ℃. The compression strength and bending strength of the SPS bulk samples at 1 000 ℃ is obviously higher than that of the SPS bulk samples at 1 100 ℃. On the base of analysis of fi＇actographies, it shows that the compression fracture transformation of the SPS Ti-45Al-5.5（Cr, Nb, B, Ta） alloy at 1 000 ℃ is intergranular rupture and that at 1 100 ℃ is intergranular rupture and cleavage fracture. The bending fracture transformation of the SPS Ti-45Al-5.5（Cr, Nb, B, Ta） alloy samples is intergranular rupture and cleavage fracture.