一种快速凝固粉末冶金高温钛合金微观组织特征研究

MICROSTRUCTURE STUDY OF A RAPID SOLIDIFICATION POWDER METALLURGY HIGH TEMPERATURE TITANIUM ALLOY

研究了一种快速凝固粉末冶金高温钛合金的微观组织及其影响因素.结果表明:热等静压(HIP)成形温度可以显著地改变钛合金粉末的显微组织,当HIP成形温度为700℃时,粉末中的α′马氏体相开始微量分解,900℃时大量分解,分解产物为等轴/板条α相和晶界β相.α+β两相区HIP成形后的显微组织主要由等轴α相、板条α相和β相组成,随着温度升高,等轴α相略有长大,板条α相的长宽比显著降低;β单相区HIP成形后的显微组织为片层组织,主要由粗大的片层α相和沿原始β晶界分布的晶间α相组成.粉末粒度越小,HIP成形后的显微组织越细小.α+β两相区HIP成形并在α+β两相区进行热处理后的显微组织主要是由等轴α相和β转变组织组成的双态组织:β单相区HIP成形并在α+β两相区进行热处理后的显微组织是由等轴α相、板条α相和β转变组织组成的三态组织;α+β两相区或者β单相区HIP成形并在β单相区进行热处理后的显微组织均为较细的网篮组织.稀土Nd含量增加,显微组织的组成没有发生变化,但基体中弥散析出的稀土相数量增加,原始β晶粒尺寸明显减小.

The high temperature titanium alloy with rare earth element Nd addition was prepared by rapidly solidified powder metallurgy （RS-PM） processing. The microstructure of RS-PM high temperature titanium Mloy has been investigated systemicMly. Microstructure study showed that the cd martensite phase in the RS powders initially decomposed at 700 ~ and vastly at 900 during the hot isostatic pressing （HIP） process. The decomposition products were equiaxed or lamellar a phase as well as grain boundary β phase. The microstructure of the specimen HIPed at the temperature in （α＋β） phase field contained equiaxed α phase, lamellar α phase and β phase. The size of equiaxed （~ phase increased while the aspect ratio of the lamellar a phase decreased when the HIP temperature increased. The microstructure of the specimen HIPed at the temperature in ~ phase field contained coarsed lamellar a phase, grain boundary a phase and ~ phase. The microstructure became finer with decreasing the powder particle size. The microstructure of the sample HIPed in the （α＋β） phase field and then heat treated in the （α＋β） phase field was bi-modal microstructurecontaining equiaxed c~ phase and ~ transformed structure. The microstructure of the sample HIPed in the ~ phase field and then heat treated in the （c~＋fl） phase field was ternary microstructure containing equiaxed a phase, lamellar c~ phase and fl transformed structure. The microstructure of the sample HIPed in the （a＋~） phase field or ~ phase field and then heat treated in the ~ phase field was basket- weave structure. The proportion of rich-Nd phases increased with increasing the Nd content, resulting in the reduction of original ~ grain size.