1940 World War II
Austenal Process Stellites Block Moulds
1950 Jet Transportation Nimonics
Colloidal Silica Simple Cores Vacuum Casting
Figure 1: Foundation Technologies 1980
I.T. Revolution
Single Crystals Structural castings Titanium casting Robot shelling Complex cores
Figure 2: Fruition Technologies
for critical components. Originally considered for restoring mechanical properties in service engine turbines, it was apparent to the industry that the process could be better applied to heal and thus eliminate internal casting porosity. The introduction was expediated following premature engine failures due to microporosity and the success naturally led to its acceptance as the guarantor of component quality. The technologies mentioned in
Figure 1 prepared the industry for success as the foremost manufacturing process for precision components operating in extreme conditions. The technologies mentioned in Figure 2 built upon the foundation processes, often
with technically spectacular
results. Two advances, among many, that represent the fruits of these earlier technologies and have made possible engineering dreams are the single crystal and titanium casting processes. Single crystals are a natural progression from directional solidification and by itself offers only a limited advantage in terms of material performance over DS. However, a single crystal does not need to have
®
alloying elements to strengthen grain boundaries, and it was this obvious fact which opened opportunities to design alloys with the capability of homogenising thermal treatments (Figure 3). Combined with aerothermal technology it became possible to design airfoils capable of service at the limits of combustion technology. Titanium and its alloys have a density around half that of nickel alloys and an intermediate temperature specific strength superior to cast nickel alloys. The principal applications at the present time are for structural casings and components not subject to extreme turbine conditions. Molten titanium is highly reactive to oxygen (it will dissolve its own oxide) and hence melting furnaces are designed to eliminate contact with refractory oxides and investment moulds prepared using chemically inert refractories.
The
success of the titanium casting industry is rightly celebrated as a triumph for foundry technology.
Although the technologies mentioned in this short paper are principally foundry related, they require the scientific expertise of metallurgists to develop the alloys, chemists to
Superalloys
Monsanto HES Ceramic Cores
1960
Fuel Crisis Cold War
D.S. HIP
1970
1990 Environmental Protection Regional Wars, E.U. Enlargement, Company consolidation
Water base shells Large DSX for IGT Process modelling Re alloys Y alloys
Environmental issues Raw material issues Intermetallics Ru alloys
2000
2010 onwards Financial crisis Pandemic
Digital technology Complex designs 3D Printing
Figure 3: This shows the creep advantage of a heat-treated single crystal (DS) blade. Both materials had the same engine experience.
develop the waxes and shell systems, mechanical engineers the machinery, mathematicians to model the processes, and production engineers to ensure quality is maintained. All of us have a passion for the industry and have made it the success it rightly enjoys.
August 2021 ❘ 11
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