Microstructrures and Mechanical Properties of Ni-Base Alloys Consolidated by Vacuum Plasma Spray (VPS) Process

Abstract

Increased demands of the aircraft jet engines have been steadily increasing the need for materials exhibiting higher strength at high temperatures. Ni-base alloys, which are highly resistant to thermal fatigue and thermal shock have been used to meet these requirements. Ni-base alloys, known for their high temperature strength up to 900°C, were deposited by the vacuum plasma spray (VPS) process. The plasma deposition process uses metal powders, offering near net shape capability with dense and homogeneous microstructures. The research described here reviews the properties of several Ni-base alloys: Ni5Mo5Al, Ni27Mo6Al and blends with Mo powders, consolidated by the VPS process. These Ni-base metals which are alloyed or blended with Mo have lower thermal expansion than the common used materials alloyed with chromium. These metals were deposited using plasma jets, varying the operational parameters and conditions. The morphology of the powder particles of the alloys has been studied prior to processing. The microstructures of the deposits were analyzed in the “as-sprayed” conditions and after post deposition treatments. Plasma deposition parameters were selected which produced dense as-sprayed structures up to 98%. Post deposition thermal processes such as HIP and sinter cycles were also explored. The deposited materials were analyzed for the degree of particle melting in the jet, deposit bulk density, mechanical properties (tensile and impact) at room temperature and at 760°C and coefficient of thermal expansion from R.T to 1100°C. Results showed that the VPS process and post deposition treatments produced dense (˜99%) Ni-alloys deposits with high strength and low coefficients of thermal expansion.