AAWSAP DIRD, Materials for Advanced Aerospace Platforms, January 2010

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A couple of costly and highly visible TMC component test failures using TSM
materials called into question the viability of TMCs. In truth, the real issue was one
of quality and not the fundamental viability of the TMC material concept.
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These failures led to extreme caution by the government, which promptly imposed
stringent quality requirements on TSM. Consequently, TSM became a serious
bottleneck for availability of TMCs with acceptable quality. As a result, numerous
large, government-funded R&D programs fell behind schedule to the point that
some were canceled and others were abandoned.
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Other, less attractive SiC fibers were being developed during this period, including
Nicalon in Japan and Sigma in the United Kingdom. Because SiC fiber and TMCs
were deemed strategic materials and neither of these alternate fibers was produced
in the United States, there was reluctance to experiment with them, and the U.S.
government occasionally prohibited their use in federally funded R&D programs.
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The issue of fiber availability became a major distraction from the real business at
hand-that is, improving the consistency and reducing the cost of the TMC product.
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In the end, TSM partially relented, but by then such limited interest in TMCs existed
that the original opportunity was lost. Furthermore, there still was no concrete
evidence that TMCs could be produced with sufficiently consistent properties that
they could be considered an engineering material (at any cost).
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In the mid-1990s, a cost study that assumed fiber availability showed that TMCs
that meet specification properties could be manufactured for about $500/lb (in 1995
$) if the use volume was about 10,000 lb/year. Finding enough low-risk, high-value
applications to consume this quantity of TMCs was not deemed possible.
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Consequently, work on TMCs halted after an investment of about $500 million of U.S.
government funds and a (presumably) comparable, but less well known private
sector (mostly independent R&D $) investment.
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One lesson from this is that a credible market and cost study should be undertaken
before embarking on a major R&D program to develop revolutionary materials such
as TMCs.
The foregoing discussion exemplifies the challenges associated with developing and
commercializing a revolutionary new materials system. New material concepts
originating from nonproduction sources such as national laboratories or research
universities should be approached with caution and never be put on the critical path of
product design. Even if a new material is vetted through an established production
source, the timing of full commercialization should be carefully examined.
Ni-base Alloys
Ni-base alloys have been considered real engineering materials for at least 40 years.
Because of their relatively low rate of strength loss with increasing temperature, Ni­
base alloys are also called "superalloys." They are commonly used at temperatures well
in excess of half of their melting point (Tm), which is the accepted useful limit for most
structural metallic materials. There is no other class of structural alloys for which this is
true. Ni-base alloys have been used in turbine engines of all types almost since their
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