Creep of low-plastic heat-resistant materials in dending

Abstract

Express method of testing the initial creep stagiess of low-plastic heat-resistant materials that work in extreme conditions using the bending scheme proposed and developed. The features of stress and deformation calculation are analyzed. The limitations of using the elastic approximation are outlined: the degree of plastic deformation of the sample should not exceed 1—1,5%. The deflection should not exceed 10% of the distance between the supports, the height should not be greater than 1/10 of the distance between the supports. Under these conditions, the first and second stages are well distinguished on the creep curves. This makes it possible to analyze the influence of phase and structural changes on the mechanisms of creep at each stage, and the conditions for the transition to stationary creep. The results of model experiments performed on TNM titanium aluminide alloys and Fe3Al powder alloy samples indicate the expediency of using the three-point bending scheme for researching the initial stagiess of creep of heat-resistant materials. Experimentally determined values of the deformation rate vary in the range έ ~ 10-5—10-8, which is the most characteristic for the creep of heat-resistant materials. For low-plastic intermetallics, the influence of temperature and loading force on creep curves was studied. The dependences deformation rate vs time on the first and second stages of creep were obtained from bending tests. Thermal activation parameters are defined for the stage of permanent creep. The proposed method allows to study the speed sensitivity and to determine the thermal activation parameters of creep. In extreme conditions of operation of low-plastic heat-resistant materials, the proposed method allows to take into account and analyze the contribution to the creep of cracking and slow destruction processes. Keywords: three-point bending test, rate of deformation, initial stages of creep,high temperature materials, thermal activation parameters.