Hardening single crystals of molybdenum and tungsten alloys by the method of internal saturation

Abstract

1. The use of carburizing, nitriding, internal oxidation, vacuum annealing, and their combinations makes it possible to form a structure of disperse segregations with specified parameters in the surface layers of single-crystal molybdenum and tungsten alloys and thus control their properties. 2. The use of nitriding (including that followed by a low-temperature vacuum annealing) is expedient for parts operating at a temperature of at most 1400–1450°C (depending on the composition of the single crystals). 3. The use of nitriding by the studied regimes for reinforcing single crystals of molybdenum and its alloys is inexpedient. 4. The use of internal oxidation for reinforcing single crystals of molybdenum alloys is expedient for parts operating at a temperature of at most 1450°C for the Mo−Nb system and at most 1650°C for the Mo−Zr system. Single crystals of alloys in the W−Zr, W−Hf, and W−Ta (together with Re) systems can also be reinforced with the help of internal oxidation. 5. A stabilizing low-temperature vacuum annealing after internal oxidation makes it possible to increase the service temperature of single crystals of the Mo−Nb−Zr−C system to 1600–1650°C. 6. Saturation in a nitrogen- and oxygen-bearing atmosphere (simultaneously or in turn) provides a layer consisting of several zones with the specified distribution of properties, including the hardness, which increase with the thickness of the part and protect it from cracking. 7. The use of the determined laws for hardening molybdenum inserts for pressure steel casting has increased their service life by a factor of 3–3.5.