„In Situ”︁ Composites for jet propulsion and stationary gas turbine applications

Abstract

Metallurgists and casting engineers focused on new composites (DSE) for high temperature applications in jet engines. Some examples of reinforced superalloys are discussed. The phase stability of microstructures has been tested using a special high thermal gradient device. For stationary gas turbines efforts in alloy development, transfer of laboratory scale to precision casting technology, and first engine tests of directionally solidified Co-Cr,C, eutectic alloy are being reported.

Control of Directional Solidification Process for Production of Gas Turbine Blades.

“…The modelling oriented itself by a set-up sketched in Fig.1(a). As a two dimensional model requires less computing time and is less complicated than a 3-dimensional model,the turbine blade shape was simplified and reduced to a cylindrical shape with a variable cross section, Fig.1.The model is based on the solution of the heat flow differential equation q/°dT/dt=k d 2 T/dX 2 +k d 2 T/dZ-2 +L(dfs -/dm)dT/dt (1) where k,c and fare thermal conductivity,specific heat and specific gravity respectIvely,L,latent heat of fusion,T,temperature,t,time,f s' fraction solidified in the mushy zone. L_…”

“…Todays jet turbines are characterized by an about 40 % improvement of total effectivity compared with gas turbines of the sixties (1).This remarkable gain was partly accomplished by selection of superalloys,but mainly by cooling techniques of blades.Vacuum melting of alloys and precision casting together _ with optimization of microstructure has led to a jump in working temperature of a few hundreds degrees K and in reaching a high fatigue resistance at both high and low temperatures° In the seventies,the limits for improving a conventional cast or forged superalloy was reached through development of alloys with Cr,Mo and other solid solution hardeners consisting of precipitates,which results in outstanding mechanical properties at high temperatures and hot as corrosion resistance (1). Directional solidification(DS) of superalloys was the next step in an attempt to reach better creep resistance by avoiding grain boundries along the axis of the blade.Remarkable progress was made by introducing DS in investment casting technology.Some jet turbines already apply directionally solidified superalloys for blades and stator vanes.DS as an advanced casting technology was optimized to form composites of extremely fine distribution of fibres with a high aspect ratio.Such an evenly distributed fibres reinforced composite could hardly be produced by mechanical manipulation.…”