EFFECTS OF THERMAL EXPOSURE ON THE TENSILE AND FATIGUE PROPERTIES OF CAST Ti-47Al-2Cr-2Nb-0.15B ALLOY
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The elevated temperature fatigue strength and room temperature tensile properties and fatigue strength of cast Ti-47Al-2Cr-2Nb-0.15B(atomic fraction, %) alloy after thermal exposure were investigated. The microstructural change of the bulk alloy and the microstructure of surface layer after 650 ℃/100 h and 800 ℃/100 h exposures were analyzed by means of XRD and SEM. The room temperature tensile ductility and fatigue strength decreased slowly with increasing exposure temperature when it is below 650 ℃, and then rapidly decreased above this temperature. Dependence of fatigue strength for the unexposed alloy with test temperature exhibits the same trend. The surface layer formed after 650 ℃/100 h exposure is an oxygen-enriched layer, while that after 800 ℃/100 h exposure is an oxide layer consisting of TiO2 and Al2O3. Such a change in the nature of the surface layer corresponds to the onset of rapid drop in mechanical proerties and fatigue strength of the alloy with increasing exposure temperature.Keywords:
Fatigue limit
Ductility (Earth science)
Surface layer
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In this study, the effect of thermal oxidation on the high cycle rotating bending fatigue behavior of Ti6Al4V alloy was investigated. Oxidation, which was performed at 600°C for 60 h in air, considerably improved the surface hardness and particularly the yield strength of the alloy without scarifying the tensile ductility. Unfortunately, the rotating bending fatigue strength at 5x106 cycles decreased from about 610 MPa to about 400 MPa upon oxidation. Thus, thermal oxidation leaded a reduction in the fatigue strength of around 34%, while improving the surface hardness (HV0.1) and yield strength 85 % and 36 %, respectively.
Ductility (Earth science)
Titanium alloy
Fatigue limit
Thermal fatigue
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Abstract : An evaluation was made of the effect of room and elevated temperatures (800 to 1200F) and times at these temperatures (0 to 30 hours) on the mechanical properties of two mortar tube alloys, AISI 4140 and AISI 4337 modified, quenched and tempered to four strength levels. The elevated temperature yield strength and ductility after exposure to the various temperatures for various times are discussed. The room temperature yield strength and -40F impact energy after exposure to various temperatures for various times are also discussed. Results of the elevated temperature tensile testing of the two alloys showed that the yield strength decreases rapidly with high temperatures. The ductility (%RA) increases with increasing temperature and remains fairly constant with time at temperature. The room temperature yield strength decreases with time after exposure at temperatures above the tempering temperature of the alloy. The -40F Charpy V-notch impact strength increases after exposure at temperatures higher than the tempering temperature of the alloy. Increasing the room temperature yield strength (by lowering the tempering temperature) does not significantly increase the elevated temperature yield strength of the alloy.
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Ductility (Earth science)
Surface Integrity
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The room temperature and high temperature tensile properties of solution and aging slate TA19 titanium alloy forging after thermal exposure at 400℃and 500℃for 100 h were tested respectively,and the effect of thermal exposure on tensile properties of TA19 titanium alloy was studied.The results indicate that the brittle layer formed on surface of TA19 titanium alloy after thermal exposure at 100℃and 500℃for 100 h had little effect on the tensile strength of the alloy,and thermal exposure effect hadn't happened.That is to say.the thermal exposure effect starting temperature of TA19 titanium alloy should he higher than 500℃.
Titanium alloy
Brittleness
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Ductility (Earth science)
Thermal Stability
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Effects of H_2-exposure, Ar-exposure and pure air-exposure at 0.1MPa at 800℃ for 24 h on tensile and bending mechanical properties at room temperature were investigated of a TiAl ally. By these exposures, both tensile and bending strength were decreased compared with the as-received not-exposed specimen. Polishing of the surface layer of the exposed specimens increased the strength to the almost same level of the as-received in the Ar-and pure air-exposures, while to the lower level in the H_2-exposure. It is found that the room temperature strength of the H_2-exposed is reduced by both the surface brittle layer and the interior brittleness.
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Effects of annealing heat treatment on microstructure,room temperature tensile properties,high temperature tensile properties and room temperature impact toughnesses of TA15 titanium alloy were studied.The results show that higher room temperature strength,high temperature strength and lower room temperature ductility,high temperature ductility,room temperature impact toughness of TA15 titanium alloy were achieved by annealing above transformation point.Under transformation point,room temperature fracture strength and high temperature fracture strength have a peak value on the annealing temperature of 860℃,room temperature ductility,high temperature reduction of crosssection area,room temperature impact toughness can be increased by increasing annealing temperature;Double annealing and triple annealing that compare with single annealing can not improve properties of TA15 titanium alloy.
Titanium alloy
Ductility (Earth science)
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This paper is an attempt to investigate the influence of aging treatment on the mechanical properties of 2618 alloy by subjecting samples of 2618 Al-alloy to different heat treatments (quenching temperatures were 520,535 and 550 ℃ respectively,aging temperature was 200 ℃ and aging time was 20 h),and performing tensile tests of 2618 Al-alloy given heat treatment at room and high temperature.The results show that aging treatment on 2618 Al-alloy affords a great amount of uniform and refined Al9FeNi-out phase,strengthened phases,and results in an obvious improvement in tensile strength of 2618 alloy at normal and high temperature.
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Brass
Structural material
Atmospheric temperature range
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The effect of long-term, elevated-temperature vacuum and lithium exposures on the mechanical properties of T-111 (Ta-8W-2Hf) is determined. Exposure conditions were for 1000 hours at 980 or 1315 C, 5000 hours at 1315 C, and a duplex temperature exposure of 1000 hours at 980 C plus 4000 hours at 1040 C. The exposures resulted in reduced tensile and creep strengths of the T-111 in the 900 to 1100 C temperature range where a dynamic strain-age-strengthening mechanism is operative in this alloy. This strength reduction was attributed to the depletion of oxygen from solid solution in this alloy.
Atmospheric temperature range
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