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

Abstract

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 alloy has been investigated systemically.Microstructure study showed that theα' 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 lamellarαphase as well as grain boundaryβphase.The microstructure of the specimen HIPed at the temperature in(α+β) phase field contained equiaxedαphase,lamellarαphase andβphase.The size of equiaxedαphase increased while the aspect ratio of the lamellarαphase decreased when the HIP temperature increased.The microstructure of the specimen HIPed at the temperature inβphase field contained coarsed lamellarαphase,grain boundaryαphase andβphase.The microstructure became finer with decreasing the powder particle size.The microstructure of the sample HIPed in the(a+β) phase field and then heat treated in the(a+β) phase field was bi-modal microstructure containing equiaxedαphase andβtransformed structure.The microstructure of the sample HIPed in theβphase field and then heat treated in the(a+β) phase field was ternary microstructure containing equiaxedαphase,lamellarαphase andβtransformed structure.The microstructure of the sample HIPed in the {a+β) phase field orβphase field and then heat treated in theβphase field was basket-weave structure.The proportion of rich-Nd phases increased with increasing the Nd content,resulting in the reduction of originalβgrain size.