Machine Casting of High Temperature Alloys for Turbine Engine Components.

摘要

A program has been initiated to evaluate the capability of machine casting for fabricating components for gas turbine engines such as compressor airfoils. The goal is to evaluate the capability of the process to produce an end product of high quality on an economic basis. During this reporting period, machine casting activity consisted of continuing equipment modifications to an already existing unit which improved die filling and decreased transfer time. Concurrently, partial assessment of process parameter effects using Rheocast Haynes Alloy 31 (X-40 cobalt-base alloy as a vehicle was performed. Machine casting preforms containing varying volume fractions of solid were injected at different die temperatures. Evaluation of the resultant product indicated that internal porosity was much lower in those parts made from initially high volume fraction solid preforms and that surface condition was improved with increasing die temperature. In addition to the above work, a heat treatment response study was performed and some limited mechanical property evaluation was conducted. Heat treatment studies indicated that long term annealing followed by aging yielded microstructures similar to those of the conventionally cast and heat treated Haynes 31 alloy, indicating the ability to largely eliminate those chemical heterogeneities peculiar to the thixotropic state of the input material. Tensile testing at room temperature and 1000 F indicated that yield strengths were higher than the nominal yield strengths for conventionally investment cast X-40 at both temperatures, while both ductility and ultimate strengths were somewhat lower.