Evaluation of Additive Friction Stir Deposition of AISI 316L For Repairing Surface Material Loss in AISI 4340

Additive technologies provide a means for repair of various failure modes associated with material degradation occurring during use in aggressive environments. Possible repair strategies for AISI 4340 steel using AISI 316L deposited by additive friction stir deposition (AFSD) were evaluated under this research by metallography, microhardness, and wear and mechanical testing. Two repair geometries were investigated: groove-filling and surface cladding. The former represents repair of localized grinding to eliminate cracks, while the latter represents material replacement over a larger area, for example to repair general corrosion or wear. The 316L deposited by AFSD exhibited a refined microstructure with decreased grain size and plastic strain, lower strength, and lower hardness than the as-received feedstock. Wear testing by both two-body abrasion and erosion by particle impingement indicated that the wear resistance of the 316L cladding was as good as, or better than, the substrate 4340 material; however, there was some evidence that the resistance to intergranular corrosion was compromised due to the formation of carbides or sigma phase. In both repair geometries, the microstructure of the substrate beneath the deposited material exhibited heat affected zones that appeared to have austenized during the deposition process, and transformed to martensite or bainite during cooling. This report constitutes an initial evaluation of a novel approach to the repair of structural steel components damaged by microcracking, wear or corrosion.

Microstructure and anti-corrosion performance of laser cladded Nb-modified Ni-based alloy coatings

In this work, Ni-based alloy coatings incorporated with Nb mass fractions of 0%, 3%, 6%, and 9% were successfully fabricated by laser cladding. The morphology, chemical composition, and phases of the obtained Nb-modified Ni-based coatings were characterized, and the effects of Nb contents on their electrochemical performance and immersion rates in 3.5 wt% NaCl solution were analyzed. The results show that the Ni-based coating with low Nb exhibits the most compact and refined microstructure, the best electrochemical passivation, and the lowest immersion corrosion rate of 3.30 × 10−3 mm/year. However, with increasing Nb content, the Laves phase is accumulated, and dendritic growth is promoted, which significantly decreases the coating passive stability and worsens the anti-corrosion performance.

Microstructural and Magnetic Behavior of Nanocrystalline Fe-12Ni-16B-2Si Alloy Synthesis and Characterization

The nanocrystalline Fe70Ni12B16Si2 (at.%) alloy was prepared by mechanical alloying (MA) of elemental powders in a high-energy planetary ball mill. Phase evolution, microstructure, thermal behavior and magnetic properties were investigated. It was found that a body-centered cubic structured solid solution started to form after 25 h milling and a faced-centered cubic structure solid solution started to form after 50 h of milling; its amount increased gradually with increasing milling time. The BCC and the FCC phases coexisted after 150 h of milling, with a refined microstructure of 13 nm and a 10 nm crystallite size. The as-milled powder was annealed at 450 °C and 650 °C and then investigated by vibrating sample magnetometry (VSM). It was shown that the semi-hard magnetic properties are affected by the phase transformation on annealing. The saturation magnetization decreases after annealing at 450 °C, whereas annealing at 650 °C improves the magnetic properties of 150 h milled powders through the reduction of coercivity from 109 Oe to 70 Oe and the increase in saturation magnetization.

Effect of Erbium on Microstructure, Hardness and Electrochemical Properties of Al-5Zn-0.03In Alloy

Al-5Zn-0.03In series alloys have been widely studied and used as sacrificial anode materials. Adding rare-earth (RE) element to Al-5Zn-0.03In sacrificial anode is the important way to improve its microstructure and properties. This paper focused on the effect of Er addition on the microstructure and properties of the Al-5Zn-0.03In-xEr alloy. Thermal analysis showed that the presence of Er in the series alloys reduced the solidification ranges and made their liquidus and solidus move to lower temperature. The microstructural analysis and hardness testing reveal that Er existed in the form of precipitation, refined the dendrites of the series alloys and improved the hardness of the series alloys. Investigation of the potentiodynamic polarization and the electrochemical impedance measurements were performed in 3.5 wt. % NaCl solution. The potentiodynamic polarization results indicated that the corrosion potential increased and the corrosion current density reduced with the increase of the Er addition. The Al-5Zn-0.03In alloy shows higher corrosion resistance with the increase of Er content. The EIS electrochemical impedance results showed that Al-5Zn-0.03In anode presented relatively uniform dissolution due to the refined microstructure by the addition of Er.

Fatigue Behavior of an Al-12.7Si-0.7Mg Alloy Processed by Extrusion and Heat Treatment

The fatigue life of a hot extruded Al-12.7Si-0.7Mg alloy under T1, T4, and T6 conditions was studied. The microstructure and tensile properties of the alloy were investigated in order to analyze the fatigue behavior. The results of the fatigue test showed that an extruded Al-12.7Si-0.7Mg alloy provided greater fatigue life compared to a cast Al-Si alloy, which was explained by the refined microstructure characterized by fine Si particles uniformly distributed in the Al matrix of fine equiaxed grains promoted by hot extrusion. The fatigue property of the alloy in T6 treatment was higher than that in the T4 and T1 conditions due to strengthening precipitation.

Investigation on the anisotropy behavior of copper strips processed by a combination of FSP and ECAP

In this study, friction stir processed (FSP) pure copper sheet was equal channel angular pressed (ECAP). The purpose was to investigate the influence of ECAP on the microstructure and mechanical properties of the FSP-treated copper sheet. The dynamically recrystallized grained structure with the average grain size of ∼13 µm was found in the stir zone of the FSP. It was also revealed that FSP caused the enhancement of ultimate tensile strength compared to that of the base metal. Also, it was observed that ECAP led to further grain refinement and a tighter distribution of grains. A refined microstructure with an average grain size of ∼ 2 µm was achieved in copper sheets through FSP, followed by ECAP. The tensile strengths of the ECAP specimens were significantly increased to about 61 and 50% compared to the strengths of base metal and FSP, respectively. An overview of the results of this study showed that combined FSP/ECAP is an effective method for the mechanical improvement of the pure copper sheets.