Analysis of In Situ Synthesis and Cross-Sectional Evolution of Wear Scars of TiAl-Ag Composites

Abstract

The need for reducing the energy consumption and volume of materials used in the aerospace industry has been driving the further optimization of the behavior of TiAl alloy under friction and wear. Therefore, investigating the micro-/nanostructures of the wear scar cross sections when TiAl-Ag composites slide against an immobile Si₃N₄ ball should help to analyze the friction and wear behaviors. Plastic deformation was observed to occur in the cross sections of the analyzed wear scar during the initial −25 min of the experiments; consequently, a work-hardened layer formed, and the friction coefficient and wear rate rapidly decreased. During the 25-60 min interval, the wear debris was refined in succession and formed a lubrication film, and the friction resistance and material loss were reduced. During the 60-120 min interval, a remarkably large amount of Ag was determined to be well distributed across the wear scar. It coincided with excellent deformation; moreover, the friction coefficients and wear rates of the TiAl-10 wt.% Ag composites were low.

Appendix

$$E_{\text{TiAl - Ag}} = E_{\text{Ag}} \cdot \phi_{\text{Ag}} + E_{\text{TiAl}} \cdot (1 - \phi_{\text{Ag}} )$$

(1)

$$a = \left\{ {\frac{{3\pi \cdot F \cdot R_{\text{TiAl - Ag}} \cdot R_{{{\text{Si}}_{3} {\text{N}}_{4} }} }}{{4\left( {R_{\text{TiAl - Ag}} + R_{{{\text{Si}}_{3} {\text{N}}_{4} }} } \right)}}\left[ {\frac{{1 - \upsilon_{{^{\text{TiAl - Ag}} }}^{2} }}{{\pi \cdot E_{\text{TiAl - Ag}} }} + \frac{{1 - \upsilon_{{{\text{Si}}_{3} {\text{N}}_{4} }}^{2} }}{{\pi \cdot E_{{{\text{Si}}_{3} {\text{N}}_{4} }} }}} \right]} \right\}^{{{\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 3}}\right.\kern-0pt} \!\lower0.7ex\hbox{$3$}}}}$$

(2)

$$\sigma_{x} = \frac{3F}{{2\pi \cdot a^{3} }}\left[ {(1 + \upsilon_{\text{TiAl - Ag}} ) \cdot (z \cdot \tan^{ - 1} (a/z) - a) + \frac{{a^{3} }}{{2(a^{2} + z^{2} )}}} \right]$$

(3)

$$\sigma_{y} = \frac{3F}{{2\pi \cdot a^{3} }}\left[ {(1 + \upsilon_{\text{TiAl - Ag}} ) \cdot (z \cdot \tan^{ - 1} (a/z) - a) + \frac{{a^{3} }}{{2(a^{2} + z^{2} )}}} \right]$$

(4)

$$\sigma_{z} = \frac{3F}{{2\pi \cdot a^{3} }}\left[ {\frac{{ - a^{3} }}{{a^{2} + z^{2} }}} \right]$$

(5)

$$F_{f} = \mu \cdot F\quad \tau_{xy} = 0\quad \tau_{yz} = 0$$

(6)

$$\tau_{zx} = \frac{{3F_{f} }}{{2\pi \cdot a^{3} }} \cdot \left[ { - a + \frac{3}{2}z \cdot \tan^{ - 1} (a/z) - \frac{{a \cdot z^{2} }}{{2(a^{2} + z^{2} )}}} \right]$$

(7)

$$\sigma_{\text{TiAl - Ag}} = \frac{\sqrt 2 }{2} \cdot \sqrt {(\sigma_{x} - \sigma_{y} )^{2} + (\sigma_{y} - \sigma_{z} )^{2} + (\sigma_{z} - \sigma_{x} )^{2} + 6 \cdot (\tau_{xy}^{2} + \tau_{yz}^{2} + \tau_{zx}^{2} )}$$

(8)

$${\text{Tkp}} = {\text{Tkw}}_{1} + {\text{Tkm}}\quad {\text{Tkw}}_{1} = {\text{Dtw}} + {\text{Tkw}}_{n}$$

(9)

where m_x, ρ_x, υ_x, φ_x, and E_x are named as additive amount, material density, Poisson’s ratio, and Young’s modulus. x is termed as sliver, TiAl alloys, or TiAl-Ag materials. a is contact radius of Hertzian. R_Si3N4 is ball radius. F_f is friction force. σ_TiAl-Ag is von Mises stress. Tkm is a thickness of micro-deformation layer. Dtw and Tkp_y are the depth and thickness of wear scars. y is known as the numbers of sliding cycles.