Creep and stress-rupture strength of rolled sheet and welded joints of niobium alloy of the system Nb-W-Mo-Zr at high temperatures

High-temperature strength characteristics of rolled sheet, welded joints, and weld metal of niobium alloy 5VMTs of the system Nb-W-Mo-Zr at 1520–2020 K and stresses comprising 0.4–1.0 of the material ultimate strength are given. It is shown that welded joints and cast weld metal under high-temperature prolonged loading conditions are the same as the basic metal, and in a number of cases they surpass it in high-temperature strength characteristics. Empirical dependences are obtained connecting the short-term material strength with its creep resistance characteristics and stress-rupture strength at temperatures above the start of dynamic recrystallization.Translated from Problemy Prochnosti, No. 12, pp. 24–32, December, 1993.     

High-Temperature Strength of Niobium Alloy 5VMTs with a Silicide-Ceramic Coating. Part 1. Short-Term Strength Characteristics

Experimental data on the short-term strength and plasticity of niobium alloy 5VMTs of the system Nb–W–Mo–Zr in its initial state, after annealing, and with a silicide-ceramic protective coating obtained by testing in vacuum, an inert atmosphere, and in air in the temperature range from 290 to 2270 K are analyzed. The process of microcrack initiation and propagation in the protective coating and matrix is investigated in high-temperature static tension. The limiting plastic strain values have been established at which the composite retains its load-carrying capacity in high- temperature aggressive and oxidizing gas atmospheres.     

Correlation Dependences between Short-Term/Long-Term Static Strength Characteristics and Creep Resistance of Tungsten at High Temperatures

Experimental data on high-temperature mechanical properties under uniaxial tension of commercially pure tungsten obtained by powder metallurgy have been analyzed. It has been found that for powder metallurgy tungsten in the high-temperature region ∼(0.5 –0.8)T_melt' there is a close correlation among the characteristics of short- and long-term static strengths and creep resistance, which are described by a single functional relation. __________ Translated from Problemy Prochnosti, No. 6, pp. 50 – 60, November – December, 2005.     

Evaluation of the Characteristics of the Plasticity of Circular Specimens of Zirconium Alloys in the Transverse Direction

We analyze the most common procedures of tensile testing of circular specimens applied in different institutions of the former USSR and compare the characteristics of the plasticity of circular specimens made of zirconium alloys obtained by different methods. This enables us to conclude that the procedures of tensile testing of circular specimens should be unified and standardized.     

Features of the Deformation and Failure of Molybdenum-Tungsten Alloy with High-Temperature Repeated Static Loading

The low-cycle strength and cyclic creep, structural changes and the nature of failure for molybdenum-tungsten alloy of the system Mo – 30%W – NbC – C prepared by powder metallurgy at 1770, 2020, and 2270 K are studied. At these temperatures a single dependence for the steady-state cyclic creep rate on the ratio of the equivalent stress to the material yield point at the corresponding temperature and a generalized low-cycle strength curve for the alloy are obtained. It is shown that the cyclic nature of the applied load accelerates directional plastic deformation and failure of powder metallurgy alloy by a factor from 1.5 to 7 compared with prolonged static loading with retention of similarity for the cyclic and static creep curves. At these temperatures the alloy essentially fails as a result of the occurrence of a critical polygonization stage. The structural changes found are in complete conformity with previously predicted features of this mechanism. Under nonstationary loading conditions the incubation period of the critical polygonization stage is shorter, which results in acceleration of creep compared with testing under stationary conditions.