Enhanced mechanical and anticorrosion properties in cryogenic friction stir processed duplex stainless steel

Further improving the wear and corrosion resistance of duplex stainless steel (DSS) without disrupting the balanced ferrite (α)/austenite (γ) ratio is worth exploring, but very challenging. Here, we explored the feasibility of utilizing solid-state friction stir processing in air (AFSP) and underwater (UFSP) to realize surface modification of DSS. Notably, we successfully developed an ultrafine-grained (UFG) structure with balanced α/γ ratio on the DSS by UFSP, which imparts both enhanced wear and corrosion resistance to the sample surface. Further, the associated microstructure evolution mechanism during FSP of DSS in both environments is systematically elucidated. The simultaneous improvement in both wear and corrosion resistance is well correlated with the resulting microstructure characteristics. This work provides a simple and cost effective pathway to achieve a synergistic increase in the wear and corrosion resistance of DSS. We anticipate that the UFSP should be applicable to many dual-phase metallic systems. 

Developing ultrafine-grained structure with balanced α/γ fraction via underwater friction stir processing enables enhanced wear and corrosion resistance of duplex stainless steel

Oxidation resistant FeCoNiCrAl high entropy alloy/AlSi12 composite coatings with excellent adhesion on Ti-6Al-4 V alloy substrate via mechanical alloying and subsequent laser cladding

Microstructure and tribological behavior of plasma spray Ni60 alloy coating deposited on ZL109 aluminum alloy substrate

Aluminum matrix surface composites (AMSCs) reinforced by various content of zirconium dioxide (ZrO2) nanoparticles and graphite (Gr) microparticles were fabricated by four passes of friction stir processing (FSP). Processing of composites reinforced by Gr particles did not lead to the sound and well-mixed composites due to a decline in the maximum experienced temperature during the process resulting from the low friction coefficient of graphite particles. Combination of graphite and zirconia particles resulted in a more homogenous dispersion of particles in the stir zone (SZ) due to a higher frictional heat generation and a lower tendency for agglomeration of nanoparticles as compared to relevant mono-composites. The occurrence of dynamic recovery (DRV) and dynamic recrystallization (DRX) along with particle stimulated nucleation (PSN) and pinning effect of the particles led to fine and equiaxed grains in the SZ as compared to coarse and elongated grains of the base metal. X-ray diffraction (XRD) analysis demonstrated formation of the Al3Zr intermetallic compounds in Al/ZrO2 nanocomposites because of in-situ reactions. Tensile tests and microhardness measurements showed that the ultimate tensile stress (UTS), yield stress (YS), and microhardness of composites gradually improved by an increase in the weight percent of the secondary phases. The UTS of Al/9 wt% ZrO2, Al/2 wt% Gr, and Al/3 wt% (Gr + ZrO2) with a hybrid ratio of (Gr/ZrO2 = 2) increased ∼42%, ∼53%, and ∼32% as compared to the base metal, respectively. Elongation of composites, especially in graphite-reinforced composites, decreased after FSP. The hybrid composite with a hybrid powder ratio of Gr/ZrO2 = 1 showed the lowest fluctuation of microhardness values because of a uniform particle distribution in the SZ. Hybrid composites with higher Gr content (Gr/ZrO2 = 2) showed greater UTS and microhardness values and lower elongation as compared to other hybrid composites. 

Tsong-Long Hwang

Papers

The role of pin eccentricity in friction stir welding of Al-Mg-Si alloy sheets: microstructural evolution and mechanical properties