The effects of environment on the dry sliding wear of eutectic Fe₃₀Ni₂₀Mn₃₅Al₁₅

Abstract

The wear of as-cast eutectic Fe₃₀Ni₂₀Mn₃₅Al_15, which consists of lamellar f.c.c. and B2 phases, was studied using pin-on-disk tribotests in four different environments: air, dry oxygen, dry argon, and a 4% hydrogen/nitrogen mixture. The counterface in all the tests was yttria-stabilized zirconia. Wear debris and wear tracks were examined in detail to investigate the surface effects during dry sliding and these were correlated with the wear properties. It was found that the wear rate was about 40% lower in tests performed under argon, compared to tests conducted in either air or oxygen. However, the wear rate was about 1000% higher when the tests were conducted in a hydrogen-containing environment. The near-surface regions of the pins were examined using transmission electron microscopy of cross-sectional specimens produced by focused ion beam milling. For tests in oxygen-containing environments, abrasive particles were produced by oxidation. These, protruded and peeled off from the matrix and mixed with the debris from the counterface, producing a combination of a two-body and three-body abrasive wear-controlled processes. In contrast, for tests under argon, plastic flow mechanisms dominated. The dramatic increase of wear in 4% hydrogen/nitrogen was due to hydrogen embrittlement, which meant that little plastic flow occurred, a feature consistent with the results of prior tensile tests.

Appendix: Calculation of contact area and contact temperature

Operating conditions:

Normal load w = 23 N	Sliding velocity V = 1 m s−1
Average friction coefficient (measured) μ = 0.15	Pin radius r = 1.5 mm

Material properties (*measured, data of zirconia is from [27])

	Zirconia (material 1)	As-cast Fe30Ni20Mn35Al15 (material 2)
Η Hardness (GPa)	12.7	3*
Ε Modulus of elasticity (GPa)	290	120*
ρ Density (kg/m3)	6100	7020*
υ Poisson’s ratio	0.24	0.33
Κ Thermal conductivity (W/m K)	1.8	9.3*
C Specific heat (J/kg K)	630

Contact geometry (assuming Hertzian contact [28])

$$ {\text{Radius\,of\,contact\,circle}}\,a = \left( \frac{3wr}{4E} \right)^{1/3} $$

where $\frac{1}{E } = \frac{{1 - \upsilon_{1}^{2} }}{{E_{1} }} + \frac{{1 - \upsilon_{2}^{2} }}{{E_{2} }}$ (E ₁, E ₂ are the moduli of elasticity for material 1 and material 2, respectively, while υ ₁ and υ ₂ are the Poisson’s ratio for material 1 and material 2, respectively)

Assume stationary pin (material 2) and moving flat Zirconia disk (material 1)

$$ \Updelta T_{\max } = \frac{1.31a\mu pV}{{\sqrt \pi (K_{1} \sqrt {1.2344 + P_{e1} } + K_{2} \sqrt {1.2344 + P_{e2} } )}} = 489^{ \circ } C $$

where the Peclet number $P_{e1} = \frac{{Va\rho_{1} C_{1} }}{{2K_{1} }} = 70$ (V is the sliding velocity of disk, while ρ ₁, C ₁, and K ₁ is the density, specific heat and thermal conductivity of material 1, respectively), and $P_{e2} = \frac{{V_{2} a\rho_{2} C_{2} }}{{2K_{2} }} = 0$ (V ₂ is the sliding velocity of pin, while ρ ₂, C ₂, and K ₂ is the density, specific heat and thermal conductivity of material 2, respectively), $p = \frac{w}{{\pi a^{2} }}$

Given that the tests were conducted at room temperature (about 25 °C), the surface temperature at the center of the Hertzian contact area was 514 °C.