Effects of the surface layer of steel samples after ball burnishing on friction and wear in dry reciprocating sliding.

The effects of ball burnishing on tribological behaviour in dry reciprocating motion have not yet been studied. This work attempts to fill this gap. The steel disc samples after milling were ball burnished. Due to ball burnishing, the average surface height decreased to 85% and the microhardness increased to 20%. Burnishing also generated the compressive residual stresses that were responsible factor to enhance the hardness of the steel surface. Trbological tests were carried out in reciprocating motion under dry sliding conditions. A 10 mm diameter ceramic ball from WC material contacted the steel disc. Ball burnishing was found to lead to improvements in disc wear and friction of the sliding pair. The maximum decreases in friction coefficient and wear volume compared to the milled sample were 39% and 85%, respectively. Samples of the lowest amplitude and high microhardness led to the highest behaviour.

The Effect of Shot Peening on Residual Stress and Surface Roughness of AMS 5504 Stainless Steel Joints Welded Using the TIG Method.

This article presents the influence of the Shot Peening (SP) process on residual stress and surface roughness of AMS 5504 joints welded using the Tungsten Inert Gas (TIG) method. Thin-walled steel structures are widely used in the aviation and automotive industries, among others. Unfortunately, the fatigue properties become worse during the welding process. Samples of 1 mm-thick AMS 5504 steel plates were first prepared using TIG welding and then strengthened by the Shot Peening (SP) process. The technological parameters of the SP process were changed in the range of time t from 2 min to 4 min and of pressure p from 0.4 MPa to 0.6 Mpa. The residual stresses were measured by X-ray diffraction in three zones: fusion zone (FZ), heat-affected zone (HAZ) and base metal (BM). The results showed that SP introduced compressive residual stresses in all of the zones measured, especially in the FZ. The greatest value of compressive residual stresses σ = -609 MPa in the FZ was observed for the maximum parameters of SP (p = 0.6 MPa, t = 4 min). The increase in value of residual stress is about 580% when compared to welding specimens without treatment. As a result of shot peening in the FZ, the mean roughness value Ra decreased in range 63.07% to 77.67% in the FZ, while in the BM increased in range 236.87% to 352.78% in comparison to specimen without treatment. Selected surface roughness parameters in FZ and BM were analyzed using neural networks. In FZ, it was demonstrated that the most correlated parameters with residual stresses are Rt and Rsk. On the other hand, in the BM zone, the most correlated parameters were Rv, Rt and Rq. This enables the estimation of stresses in the welded joint after SP on the basis of selected roughness parameters.