Study on the Beneficial Effects of Duplex Aging on Microstructure Phenomena Determining the Fatigue life of the Metastable β-titanium Alloy Ti 38-644
The use of highly β-stabilized titanium alloys in applications requiring high strength is restricted due to the proneness to the formation of precipitate-free zones and α phase layers along β grain boundaries. Although duplex aging is commonly known to be a proper technique in order to enhance fatigue properties of highly β-stabilized titanium alloys by diminishing these microstructure phenomena,a detailed description how to obtain accurate heat treatment parameters is still rare. In the present study a duplexaging cycle was designed. An extensive investigation of microstructure effects on tensile and fatigue properties in the metastable β titanium alloy Ti 38-644 (β-C) was conducted. Taking the prior working history into account, corresponding heat treatment parameters in terms of annealing times and temperatures had been specified. The microstructure response of β-C on each particular heat treatment step was monitored by applying optical and electron microscopy,hardness measurements and comparative tensile tests. The results revealed the beneficial effects of the duplex-aging cycle introduced in the present study. A superior fatigue limit of 745MPa at a limiting number of loading cycles of N=2·106 has been determined. As opposed to the directaged material all duplex-aged samples showed surface related fatigue crack initiation. Comparing the fracture surfaces of direct- and duplex-aged β-C a transition of the tensile fracture mode from intergranular to transgranular was observed accompanied by a gain in ductility. It seems,that the microstructure phenomena controlling the behaviour of β-C under tensile load do also determine the resistance of the material to fatigue crack growth. Key to success is a completely recrystallized β microstructure enabling a homogeneous distribution of the strengthening α phase and the prevention of the formation of grain boundary α phase. Therefore, thorough attention must be paid when specifying time and temperature for the solution-annealing and the pre-aging treatment.
Duplex aging beta-C precipitate-free zones heat treatment.
Ali El-Chaikh Peter Schmidt Hans- J. Christ
Institut fur Werkstofftechnik,Universit(a)t Siegen D-57068 Siegen,Germany
国际会议
The 12th World Conference Titanium(第十二届世界钛会 Ti-2011)
北京
英文
745-749
2011-06-19（万方平台首次上网日期，不代表论文的发表时间）