查看更多>>摘要：The micro-textures fabricated on the substrate surface of coating are a feasible method to improve the interfacial adhesion of the coating. This research proposes an ultrasonic rolling texturing method, and for the first time reveals how different ultrasonic rolling texturing process parameters (including air pressure, step distance, and feed speed) impact the bonding properties of AlTiN coating. The texture profile, surface morphology, hardness, elasticity modulus, and surface stress state are investigated. Then, the scratch tests are implemented to study the adhesion properties of these textured AlTiN coatings. Results showed that periodic micro-grooves were controllably fabricated, accompanied by high compressive stress and increased surface energy on AISI 5140 steel surface by ultrasonic rolling texturing. The surface morphologies and mechanical properties of the textured surface were strongly dependent on the texturing parameters. And the ultrasonic rolling textured substrate was conducive to the coatings in terms of interfacial contact area, wettability, surface energy, hardness, and residual stress, which could enhance the interfacial adhesion of the coating-substrate. The critical failure loading force of all textured coatings (FN = 43–59.35 N) exhibited higher value in comparison with the polished coating (FN = 37.91 N), demonstrating that ultrasonic rolling texturing presented a great potential in the fabrication of high precision micro-textures for enhancing the interfacial bonding properties of coatings. Furthermore, the enhancement mechanism for the ultrasonic rolling texturing on the AlTiN coating adhesion was discussed. The developed texturing method supports the application of hard coatings on mechanical parts such as molds, bearings, etc.
查看更多>>摘要：This study aims at investigating the possibility of fabricating IN625 and IN718 Ni-based superalloys with acceptable room temperature fatigue lives using the laser powder bed fusion (LPBF) process. For this purpose, several test coupons were printed and compared in terms of (i) density, (ii) tensile strength, (iii) surface roughness, and (iv) residual stress to find the optimum sets of process parameters utilized to print fatigue test specimens. Fatigue test was performed on the as-built and shot-peened specimens at multiple stress levels and compared to their wrought counterparts. The fatigue results were scrutinized by discussing the contributing factors, such as (i) surface roughness, (ii) residual stress state and magnitude, (iii) grain and sub-grain structure, and (iv) non-equilibrium phases in the microstructure. The fatigue life of both superalloys in as-built condition was inferior to their unnotched wrought counterparts, though exceeding the notched ones. After shot peening, the maximum stress level at infinite life for IN625 was the same as its unnotched annealed wrought counterpart. However, for shot-peened IN718, the fatigue life was still lower than that of the solution-annealed and aged wrought specimen in unnotched condition due to the absence of γ′ and γ′′ strengthening agents. This study suggests that the LPBF fabricated IN625 in the shot-peened state can be reliably used as a substitute for annealed and wrought IN625 counterparts without the need for surface smoothening or heat treatments. Regarding the shot-peened IN718, its lower fatigue life has to be considered in the design stage upon skipping the heat treatment.
NSTL
Elsevier