Influence of Cold, Warm and Plasma Sprayed Layers on High-Cycle Fatigue Properties of Steel Specimens

摘要

Commercial-grade titanium powder was deposited onto steel specimens using four thermal spray technologies: plasma spray, low-pressure and portable cold spray, respectively, and warm spray. The specimens were then subjected to strain controlled cyclic bending test in a dedicated in-house built device. The crack propagation was monitored by observing the changes in the resonance frequency of the samples. A stop-condition corresponding to approximately 40-60% specimen cross-section damage was used to define the fatigue performance of the specimen. The corresponding number of cycles was considered the main performance indicator. It was found that the grit-blasting procedure did not alter the fatigue properties of the steel specimens considerably (5% increase), while deposition of the coatings via all technologies significantly increased the measured fatigue lives. The three high-velocity technologies led to a relative lives of 202% (low-pressure cold spray), 220% (portable cold spray), and 383% (warm spray) and the deposition using plasma spray led to an increase of relative lives to 316%.The increase could probably be attributed to a combination of the presence of a homogeneous fatigue resistant coating and induction of peening stresses into the substrates via the impingement of the high-kinetic energy particles (cold sprays and warm spray). Given the intrinsic character of the plasma jet (low-velocity impact of semi/molten particles), the influence needs to be attributed to a different mechanism.