Effect of shot peening on the residual stress distribution in two commercial titanium alloys

The residual stress distribution in two commercial titanium alloys, the near-alpha IMI-685 and the alpha-beta IMI-318, have been determined using the method of drilling holes for the machined and polished as well as the machined, polished and shot-peened conditions. The residual stresses were always compressive and their peak values for both alloys were similar. However, the stress distribution patterns were different and this could have implications for the fatigue behaviour of the alloys.     

Influence of heat treatment on the strength characteristics of titanium alloys under static and cyclic loads

G. V. Karpenko Physicomechanical Institute, Academy of Sciences of the Ukrainian SSR, Lvov. Translated from Problemy Prochnosti, No. 5, pp. 95–97, 123, May, 1987.     

Effects of ultrasonic impact treatment on weld microstructure,hardness, and residual stress

Layered ultrasonic impact treatment (LUIT) was used on V-groove welds in 55?mm Q345 steel plate. Two welds were prepared, one by conventional gas metal arc welding (GMAW) and the other by GMAW and LUIT, where impact treatment was performed at nine stages during filling of the 28-pass weld. Microstructure, hardness, and residual stress in the welds were compared. While residual stress is very similar, there are significant differences in microstructure and hardness. The LUIT weld has mainly equiaxed grains and uniform hardness, while the conventional weld has columnar grains and a hardness gradient. It appears that beads in the LUIT weld did not exhibit columnar grain growth, and instead equiaxed grains grew from the fusion boundary into the weld.     

Gas impregnation of titanium alloys in heat treatment in a static atmosphere of argon

Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 23, No. 4, pp. 38–43, July–August, 1987.     

Interfacial structure, residual stress and adhesion of diamond coatings deposited on titanium

The interfacial structures of diamond coatings deposited on pure titanium substrate were analyzed using scanning electron microscopy and grazing incidence X-ray diffraction. Results showed that beneath the diamond coating, there was one titanium carbide and hydride interlayer, followed by a heat-affected and carbon/hydrogen diffused Ti layer. Residual stress in the diamond coating and TiC interlayer under different process parameters were measured using Raman and X-ray diffraction (XRD) methods. Diamond coatings showed large compressive stress on the order of a few giga Pascal. XRD analysis also showed the presence of compressive stress in the TiC interlayer and tensile stress in the Ti substrate. With increasing deposition duration, or decreasing plasma power and concentration of CH₄ in gas mixture, the compressive residual stress in the diamond coating decreased. The large residual stress in the diamond coating resulted in poor adhesion of the coatings to substrate, but adhesion was also related to other factors, such as the thickness and nature of the TiC interlayer, etc. A graded interlayer design was proposed to lower the thermal stress, modify the interfacial structure and improve the adhesion strength.     

Increasing the heat resistance of titanium alloys by alloying

Translated from Fiziko-Khimicheskaya Mekhanika Materialov, No. 1, pp. 120–121, January–February, 1989.     

Improvement of structure and mechanical properties of cast titanium alloys using rapid heat treatment

The possibility of rapid heat treatment (RHT) application to titanium castings has been studied. It was shown that such treatment provides a significant improvement of intragrain structure and mechanical properties of cast ( + β)-titanium alloys.     

Interaction between cyclic loading and residual stresses in titanium matrix composites

Metal matrix composites are gaining popularity for applications where high performance materials are needed. Titanium matrix composites (TMCs) continuously reinforced by silicon carbide fibres are under development for applications in aeroengines. Their use in blades, rings and shafts promises a significant weight reduction and performance improvement due to their high specific strength and stiffness. To obtain the whole capabilities of the material not only advanced processing techniques but also post-processing treatments are necessary. A detailed analysis of the residual stress development during cyclic loading leads to the necessity of residual stress modifications to optimise the fatigue behaviour of TMCs. Since the aerospace industry requires high reliability of the materials used, models for predicting failure and life time are of special interest. Predictive models based on the properties of the single constituents of the composite are most suitable to reduce the number of experiments and to develop methodologies to improve specific mechanical properties. Nevertheless, both experiments on the single constituents as well as on the composite are necessary to validate the model. A previously developed rheological model is used to assess different post-processing procedures to improve the fatigue behaviour of a titanium matrix composite. The usage of the model and experiments on the system SCS-6/Ti-6Al-2Sn-4Zr-2Mo are presented.     

Effect of thermal annealing on the microstructure,mechanical properties and residual stress relaxation of pure titanium after deep rolling treatment

The aim of this paper was to investigate the effect of thermal annealing on the microstructure, mechanical properties, and residual stress relaxation of deep rolled pure titanium. The microstructure and mechanical properties of the surface modified layer were analyzed by metallographic microscopy, transmission electron microscope and in-situ tensile testing. The results showed that the annealed near-surface layer with fine recrystallized grains had increased ductility but decreased strength after annealing below the recrystallization temperature, where the tensile strength was still higher than that of the substrate. After annealing at the recrystallization temperature, the recrystallized near-surface layer had smaller grain size, similar tensile strength, and higher proportional limit, comparable to those of the substrate. Moreover, the residual stress relaxation showed evidently different mechanisms at three different temperature regions: low temperature (T?≤?0.2?T_m), medium temperature (T?≈?(0.2?0.3)?T_m), and high temperature (T?≥?0.3?T_m). Furthermore, a prediction model was proposed in terms of modification of Zener-Wert-Avrami model, which showed promise in characterizing the residual stress relaxation in commercial pure Ti during deep rolling at elevated temperature.     

Features of reaction stress generation in alloys based on titanium nickelide

Generation of reaction stresses is studied in relation to the magnitude of prior strain _pr, the part of it recovered, shape memory strain _SME, and method of assigning it in alloys based on titanium nickelide exhibiting different kinetic development of the shape memory effect, structural type, and phase transition temperatures. It is shown that curves for the dependence of maximum reaction stresses on shape memory strain _SME may either almost agree, independent of the method of assigning _pr and the nature of martensitic transformation, or be placed much lower than the tensile diagram for material in the austenitic condition.Translated from Problemy Prochnosti, No. 3, pp. 60–63, March, 1990.     

Effects of cooling rate and heat treatment on the microstructure of iron-based titanium carbide composites

The microstructural response of iron-carbon-TiC components produced by a liquid route to changes in cooling conditions and post-solidification heat treatments has been investigated. Heat treatments of pure Fe-TiC composite materials have been found to produce only minor changes in the TiC morphology and distribution with reduction in hardness resulting from some TiC precipitation and depletion of the iron matrix of titanium and carbon. As-cast composites containing Fe-2.4% C/10% TiC and Fe-3.27% C/10% TiC exhibit a white cast iron matrix containing dispersed TiC. Subsequent heat treatment of this material at 750° C renders the matrix malleable, replacing the cementite by free graphite with no apparent alteration to the TiC morphology or distribution.