The influence of maximum temperature of heating on the thermal fatigue of nickel heat-resistant alloys under thermocyclic tests

The analysis of high temperature resistance alloys thermocyclic tests show that the lifetime Np is less when maximum temperature Тmax in test cycles (ΔТ=Тmax-Тmin) is more 900°С. In most test cases thermal cycle contents the plastic deformation. The cooling half-cycle includes three temperature intervals: first – where heating halfcycle compression stress decrease take place, second – where tension stresses are increased to yield stress σ02 and plastic deformation begin, and third interval - plastic deformation region, which is finished at minimum temperature of cycle Тmin. The stress decrease interval length depends from value of stress, which is reached in precede heating half-cycle and, as we consider, equal σ 02(Tmax). High temperature resistance alloys are characterized by yield stress σ 02 sharp decrease at temperatures which is more 900°С. Because at cooling from temperatures, which is lower 900°С, stresses, which must to decrease, are larger on one third them at 1000°С and on half them at 1100°С. Therefore third temperature interval is shorter at cooling from temperature which is more 900°С, plastic deformation is more and lifetime NP smaller.