The manufacture of gas turbine compressor components by Metal Injection Moulding

Gas turbine compressor components manufactured from nickel base alloys have traditionally been precision die forged in sequential thermo-mechanical processing operations in order to achieve the desired geometry and mechanical properties. Metal Injection Moulding (MIM) is a competing three dimensional forming technology with proven applications in both the automotive and medical industries for producing industrial quantities of small, net shaped components. To date, the Metal Injection Moulding process has had limited exposure as a manufacturing process for gas turbine compressor components. The aim of this research thesis is to establish if the Metal Injection Moulding process can be used to manufacture compressor components of equivalent mechanical properties to those manufactured by conventional processing methods. In order to achieve this aim a rigorous program of metallurgical testing and analysis has been developed. The objectives of this program focus on determining the key material properties from each of the competing manufacturing processes. The methodology used to assess the merits of each process was based upon comparative back to back testing trials using both representative components and material test bars. The test results demonstrate that while the mechanical properties of the Injection Moulded 718 alloy can be improved by subsequent thermo-mechanical processing, there remains however a significant deficit in the strength, ductility and creep properties compared to the wrought 718 alloy datum results. The recommendations which have been made as a result of this research focus on improvements to the condition of supply of the powdered 718 alloy and to the controls associated with the Metal Injection Moulding process in order to minimise process variation. Standardisation of the mechanical testing methodology including the test piece geometry is also considered necessary in order to achieve a more meaningful comparison to published historical test data and allow wider industry corroboration of test results conducted in accordance with aerospace standards.