Авіаційно-космічна техніка та технологія (Oct 2021)
Ways to increase the properties of blots of gas turbine engine parts from heat-resistant titanium alloys obtained by direct laser growth
Abstract
Today, additive technologies for the production of billets from heat-resistant titanium alloys are used in aircraft engine building and the aerospace industry. However, the mechanisms of structure formation and the level of mechanical properties in such blanks are poorly understood and are of interest. Currently, available data are not sufficient for the confident application of additive technologies in the production of aircraft engines. This paper evaluates the microstructure and substantiates the possibility of improving the mechanical properties of workpieces of GTE parts made of VT20 titanium alloy, obtained by laser-powder additive surfacing. For research, workpieces with a size of 215x120x4 mm 120x85x14 mm were grown. As a "building" material, a powder of spherical shape of particles was used, the chemical composition of which corresponds to the alloy VT20. The research results showed that during laser-powder growth in the VT20 alloy, the formation of "hardening" structures is observed, due to the accelerated heat removal into the previously formed layer of cast metal. In this regard, the strength of the alloy sharply increases, and its impact toughness and relative narrowing decrease. Note that stress relief annealing after growing (T = 750 ± 10 ° C, holding time - 1.5 ... 2.0 h.) does not significantly affect the level of mechanical properties. When the annealing temperatures rise to critical levels, significant structural changes are observed in the VT20 alloy, which in turn affects its mechanical properties. Based on the analysis of microstructures and the results of mechanical tests after distinct types of heat treatment (800 ° C, 850 ° C, 920 ° C, holding time - 60...75 min.), it was found that an increase in the plastic properties of the VT20 alloy is observed when the samples are heated to temperatures close to the temperature of the polymorphic transformation (960...1000 ° C). Annealing of workpieces after surfacing according to mode T = 920 ± 10 ° C, holding time - 60...75 min. allows to somewhat reduce the strength characteristics of the VT20 alloy, while increasing its impact strength and relative narrowing.
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