2Al-2Mn-Ti合金および工業用純チタニウムの高温疲労強度について

Abstract

Titanium and its alloy are widely used as structural materials because of their excellent corrosion-resistance and heat-resistance properties.This report deals with the unnotched and notched fatigue strengths of 2 Al-2 Mn-Ti alloy and some commercially pure titaniums in a high temperature range from 20°C to 600°C, as well as the internal heating phenomenon at a room temperature of commercially pure titanium which affects their fatigue strength.The high temperature fatigue tests were conducted on Ono's high temperature fatigue tester (3000rpm) and a Krouse high speed high temperature fatigue tester (5000rpm). The fatigue tests at a room temperature are conducted on Ono's fatigue tester and a Schenck's vibrating fatigue tester.The high temperature mechanical properties of the specimens are shown in Fig. 3-7 and the notched and unnotched fatigue strengths in a high temperature at 107 cycles are also shown in Fig. 14, respectively.The unnotched and notched fatigue strengths of 2 Al-2 Mn-Ti alloy decreased remarkably from the values of room temperature up to 100°C, and in a range from 150° to 300°C, those rates steadily changed, and in the case of further temperature, those rates increased again.The unnotched fatigue strength of commercially pure titaniums decreased remarkably with the increase of temperature up to 200°-300°C, and those rates changed smoothly in further temperatures. The high purity specimen shows lower fatigue strength than that of lower purity specimen. The reduction percentage of fatigue strengths and fatigue strength reduction factor (3.0 theoretical stress concentration) of each specimen are shown in Fig. 15 and 16.In the high temperature fatigue tests, an unnotched specimen tested in high stress levels induced internal heating phenomenon and the specimen changed their colour due to generated heat. The authors presumed the temperature of generated heat from the degree of their discolouration of specimen and examined the modified S-N curves as shown in Fig. 17.Internal heating phenomenon at a room temperature of commercially pure titanium is more remarkable as to the high purity material than in the case of lower purity, and the maximum temperature of generated heat is related to repeated stress levels as shown in Fig. 22, and also the size effect of specimen influences on their phenomenon as shown in Fig. 27.