Abstract
For economic and environmental reasons, dry forming is of increasing interest due to the shortening of process chains, cost savings and reduction of environmental pollution. The aim of these investigations is to examine to what extent chemical vapor deposited (CVD) diamond coatings are suitable for dry forming of aluminum and to identify the surface topology requirements for a low friction coefficient and low wear. Nine different surface topologies of CVD diamond coatings were tested in an oscillating ball-on-plate tribometer test against aluminum balls with a Hertzian contact stress of 759 MPa and 99,900 cycles. It could be concluded that the peak material volume (Vmp) of the diamond coating is the most important factor for achieving a low abrasion of aluminum as well as a low friction coefficient against aluminum. The Vmp should be smaller than 0.04 ml/m2. Microcrystalline CVD diamond with a post-treated surface has great potential for dry forming of aluminum.
Highlights
Dry forming is of increasing interest for both economic and environmental reasons
The aim of these investigations is to examine to what extent chemical vapor deposited (CVD) diamond coatings are suitable for dry forming of aluminum and to identify the surface topology requirements for a low friction coefficient and low wear
The coefficients of friction of the CVD diamond coatings clearly show the influence of the coating surface in dry tribological contact with aluminum
Summary
Dry forming is of increasing interest for both economic and environmental reasons. Different approaches already lead to a possibility of dry forming. Bhushan et al.[1] showed a decreasing coefficient of friction with decreasing roughness in the oscillating ball-on-plate test of aluminum balls against differently smoothly polished CVD diamond coatings. This thesis that both the wear rate and the coefficient of friction decrease with a decreasing surface roughness is supported by several publications. The nanocrystalline CVD diamond coatings with a roughness of Ra 30 nm lead to the highest coefficient of friction of 0.57 This clearly shows that the roughness [Ra or the root mean square deviation (Rq)] is not a suitable parameter for establishing a clear correlation with the coefficient of friction and the wear rate
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