Creep Behavior of <I>In Situ</I> Synthesized 7715D Titanium Matrix Composite

Abstract

TiB and TiC reinforced titanium matrix composite was in situ synthesized by consumable vacuum arc remelting and hot-forging based on reaction between titanium, B 4 C powder and graphite powder. The phases were analyzed through X-ray diffraction. The microstructure was examined by means of optical microscopy (OM) and scanning electron microscopy (SEM). Creep behavior was tested at three temperatures: 600 C, 650 C and 700 C respectively within a stress range 100$350 MPa. Class I solution behavior was observed and true stress exponent n ¼ 3:5 was obtained for the composite. Threshold stress, load transfer and micro-structural strengthening are considered for reasonably explaining the creep behaviour. It is concluded that strengthening mechanism can be owed to co-effect of all the three factors. True activation energy equal to 343 kJ/mol was obtained after compensation by threshold stress.

Effect of Heat Treatment on Creep Properties of in situ Synthesized (TiB+La2O3)/Ti Composite

“…The relationship between creep rate and stress and temperature can be expressed by the following Equations (1-3) (Li et al, 2008;Wang et al, 2009Wang et al, , 2019:…”

“…The apparent stress exponents of matrix alloy are lower than those of TMCs. Wang et al (2009) have reported that the creep behavior can be divided into two categories: one creep behavior controlled by viscous dislocation sliding is different; other creep behavior controlled by dislocation climb. Koike et al (1995) report that dislocation sliding is dominant when the stress exponent is 3.5, when the stress exponent is 4.6, dislocation climb is governing.…”

“…Threshold stresses of TMCs after heat treatment are shown in Figure 10. The value of true stress exponent n is usually considered as stress exponent of matrix alloy (Wang et al, 2009;Xiao et al, 2009). The stress exponent n value of matrix alloy is all close to 4.5, which is considered that creep mechanism is the typical dislocation climbing (Hofmann et al, 1998).…”

“…TiB reinforcements take load from the matrix, and then break. A coefficient β can be indicated the effect of load transfer by following equations (Wang et al, 2009):…”

“…The β value is 0-1(the β value of matrix is 0). The stress of TMCs and load transfer coefficient can be expressed as the following equations (Wang et al, 2009;Xiao et al, 2009):…”