“Some would consider Jethete M152 to be an HRSA, but in our eyes it’s just a low-carbon martensitic stainless steel,” he said. Minich also noted that not all alloys called HRSAs actually fill the bill. Some HRSAs are also used in medical device manufacturing, not necessarily for heat resistance but for bio-compatibility as well as strength, stiffness and corrosion-resistance properties. “Oil, gas and their derivatives and anything else that is corrosive and abrasive that needs to be stored, processed or transported at high pressure and temperature tend to require the strength and resistance to corrosion at elevated temperatures that only Ni-based alloys can offer,” said Minich. However, the materials are also widely used in the oil and gas industry. Probably the most prominent application for HRSAs is their use in the aerospace and defense industry, in the form of components for turbine engines used in jets, rockets and missiles. Here’s the latest on how cutting tool manufacturers are making the job easier. The same resistance to heat (and increasing yield strength with temperature) that makes HRSAs desirable for such applications is what makes them a challenge to machine. It seems to be an anomaly-hence the name. He is referring to when yield strength increases with temperature, contrary to most materials that get softer as they get hotter, or lower yield strength. “ HRSAs as all nickel- and cobalt-based alloys that exploit the yield-strength anomaly," noted Alex Minich, applications engineer at toolmaker Greenleaf Corp., Saegertown, Pa. Ingersoll’s CERASFEED indexable ceramic high-feed end mill in action at the company’s Rockford, Illinois, technical center. Modification of the low-temperature, ultraviolet-enhanced chemical vapor deposition process used to apply interface coatings to the fiber preform was also required to accommodate the high preform thickness.Heat-resistant superalloys (HRSAs) are nickel and cobalt-based alloys prized for applications that call for strength, resistance to corrosion and oxidation, and resistance to contact wear needed at extremely high temperatures. However, processing of thick-section components required modification of the conventional process conditions, and the means by which the large amount of molten metal is introduced into the fiber preform. This prevents over-infiltration of the outer surface plies, which can lead to excessive residual porosity in the center of the part. The melt infiltration method requires no external pressure. Densification to <5 vol% porosity is a one-step process requiring no intermediate machining steps. Infiltration occurs from the inside out as the molten metal fills virtually all the available void space. A molten refractory metal is then infiltrated and reacts with the excess carbon to form the carbide matrix without damaging the fiber reinforcement. Melt processing first involves infiltration of a fiber preform with the desired interface coating, and then with carbon to partially densify the preform. Ultramet-modified fiber interface coating and melt infiltration processing, developed previously for thin-section components, were used for the fabrication of CMCs that were an order of magnitude greater in thickness. A method was developed for producing thick-section, continuous fiber-reinforced ceramic matrix composites (CMCs).
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