Evaluation of Heat Checking and Washout of Heat Resistant Super-alloys for Die Insert Applications (Case Western Reserve University)
This study investigated the potential of special types of nickel-base alloys as die casting die
materials. Researchers evaluated materials and coatings, including heat resistant superalloys,
for use as inserts in die casting of aluminum alloys. The mechanisms of thermal fatigue crack
nucleation and propagation in superalloys were studied and compared to thermal fatigue cracking
of steels. The project developed a test that determined the erosion resistance of these materials
in a stream of molten A-380. A feature common to all coatings is the presence of pinholes from
manufacturing which become failure sites by undercutting. The molten aluminum penetrates the coating
through the pinhole and creates a crate underneath. The coating loses its support from the substrate and fails locally while creating a larger pinhole.
The percentage of soldering area with aluminum on pin impinging surface (PSA) and weight of soldered aluminum on pin surface (WSA) can be used accurately and conveniently for evaluating the resistance to soldering. Weight loss of pin (WL) or volume loss of pin (VL) can be used to evaluate the resistance to washout accurately and conveniently. Of the superalloys tested, Anviloy1150 has the best resistance to soldering and washout, followed by Mo-785, Ti-6Al-4V, hard-H13, soft-H13, Ni718 and cast iron. Copper base alloy has the worst. The final report describes the mechanism of soldering and washout that has been proposed.
Good coatings practices are essential in ensuring a high performance coating.