Investigation of Thermal Stability of Microstructure and Mechanical Properties of Bimetallic Fine–Grained Wires from Al–0.25%Zr–(Sc,Hf) Alloys

Thermal stability of composite bimetallic wires from five novel microalloyed aluminum alloys with different contents of alloying elements (Zr, Sc, and Hf) is investigated. The alloy workpieces were obtained by induction-casting in a vacuum, preliminary severe plastic deformation, and annealing providing the formation of a uniform microstructure and the nucleation of stabilizing intermetallide Al3(Zr,Sc,Hf) nanoparticles. The wires of 0.26 mm in diameter were obtained by simultaneous deformation of the Al alloy with Cu shell. The bimetallic wires demonstrated high strength and improved thermal stability. After annealing at 450–500 °C, a uniform fine-grained microstructure formed in the wire (the mean grain sizes in the annealed Al wires are 3–5 μm). An increased hardness and strength due to nucleation of the Al3(Sc,Hf) particles was observed. A diffusion of Cu from the shell into the surface layers of the Al wire was observed when heating up to 400–450 °C. The Cu diffusion depth into the annealed Al wire surfaces reached 30–40 μm. The maximum elongation to failure of the wires (20–30%) was achieved after annealing at 350 °C. The maximum values of microhardness (Hv = 500–520 MPa) and of ultimate strength (σb = 195–235 MPa) after annealing at 500 °C were observed for the wires made from the Al alloys alloyed with 0.05–0.1% Sc.

Investigation of Effect of Preliminary Annealing on Superplasticity of Ultrafine-Grained Conductor Aluminum Alloys Al-0.5%Mg-Sc

Effect of preliminary precipitation of Al3Sc particles on the characteristics of superplastic conductor Al-0.5%Mg-X%Sc (X = 0.2, 0.3, 0.4, 0.5 wt.%) alloys with ultrafine-grained (UFG) microstructure has been studied. The precipitation of the Al3Sc particles took place during long-time annealing of the alloys at 300 °C. The preliminary annealing was shown to affect the superplasticity characteristics of the UFG Al-0.5%Mg-X%Sc alloys (the elongation to failure, yield stress, dynamic grain growth rate) weakly but to promote more intensive pore formation and to reduce the volume fraction of the recrystallized microstructure in the deformed and non-deformed parts of the aluminum alloy specimens. The dynamic grain growth was shown to go in the deformed specimen material nonuniformly–the maximum volume fraction of the recrystallized microstructure was observed in the regions of the localization of plastic deformation.

Modulation of Multiple Precipitates for High Strength and Ductility in Al-Cu-Mn Alloy

The category and morphology of precipitates are essential factors in determining the mechanical behaviors of aluminum alloys. It is a great challenge to synthetically modulate multiple precipitates to simultaneously improve strength and ductility. In the present work, by optimizing the precipitations of the GP zone, θ’-approximant and θ’ phase for an Al-Cu-Mn alloy, a high tensile strength of 585 MPa with large elongation of 12.35% was achieved through pre-deformation and aging. The microstructure evolution pattern was revealed by detailed characterizations of scanning electron microscopy and transmission electron microscopy. It was found that such high tensile strength of the samples was due to a combination of strengthening by the high density of dispersive fine precipitates and dislocations, and the high elongation to failure was primarily attributed to the multimodal precipitates and elimination of precipitation-free zones along the grain boundaries. The strategy proposed here is a promising way of preparing ultra-strong Al-Cu-Mn alloys.

Effects of Ce-Rich Misch Metal on the Microstructures and Tensile Properties of as-Cast Mg-7Al-3Sn-1Zn Alloys

The effects of small amounts of Ce-rich misch metal (Mm: 0.5, 1.0 and 2.0 wt.%) addition on the microstructure and tensile properties of as-cast Mg-7Al-3Sn-1Zn wt.% (ATZ731) alloy have been investigated. The addition of Mm restricts the formation of the Mg17Al12 phase but greatly promotes the Al4Mm phase. The proper Mm addition enhances the strength and ductility of ATZ731 alloys at both room temperature (RT) and 175 °C. ATZ731 alloys with 1.0 wt.% Mm addition exhibit an advantageous combination strength and ductility, with the ultimate tensile strength (UTS), 0.2% yield strength (YS) and elongation to failure (Ef) at 175 °C of ~148 MPa, ~102 MPa and ~28%, improved by ~14.7%, ~24.3% and ~53.8%, respectively, compared to those of ATZ731 alloy. This enhancement is primarily owing to the refined microstructures and the high thermal stability of Al4Mm at the elevated temperature in contrast with that of the Mg17Al12 phase. The fracture modes are also discussed.

Powerful Material Technology Removes Barriers

Strengthening materials through grain refinement often results in reduced ductility necessitating means to augment their elongation to failure for engineering applications. Grain boundary engineering (GBE), encompassing novel thermo-mechanical processing has shown promise of simultaneously enhancing both strength and ductility of materials and fracture behavior, especially with low stacking fault energy materials. The ultrahigh strength and reasonable ductility originate from dislocations being effectively blocked at the nano-twinned boundaries resulting in dislocation accumulation and entanglement. This necessitates the careful design of alloys and nano-composites, an effective harnessing of these unique sub-micron features to the benefit of engineering downhole tools for strategic applications. Enabled by these novel material developments, here we present two such articles for the unconventionals. First, a frangible barrier to abet placement of casings and liners through trapping an air column below the barrier while supporting a fluid column in the casing above, providing an up-thrust, a buoyant force that significantly reduces drag and lateral casing weight during placement. This is a viable concept because "shales don't kick". Second is the unmet need for a clean perforating tunnel allowing reduced fluid friction thus better reservoir connectivity. This has been achieved through the development of a novel shape charge with a reactive liner which during the detonation event, additionally generates reactive metallic glassy phase(s) and high entropy alloy complex(s) and their segregation in the deposited jet debris that lines the perf-tunnel. During flowback, reaction with aqueous fluids selectively etch these phases and stimulates the disintegration of the impervious skin on the perf-tunnel into fine particulates subsequently removing them, leaving behind a clear, clean tunnel.

Heat Treatments for Stress Relieving AlSi9Cu3 Alloy Produced by Laser Powder Bed Fusion

The present work explores the effect of a stress relieving heat treatment on the microstructure, tensile properties and residual stresses of the laser powder bed fused AlSi9Cu3 alloy. In fact, the rapid cooling rates together with subsequent heating/cooling cycles occurred during layer by layer additive manufacturing production make low temperature heat treatments desirable for promoting stress relaxation as well as limited grain growth: this combination can offer the opportunity of obtaining the best compromise between high strength, good elongation to failure and limited residual stresses. The microstructural features were analysed, revealing that the high cooling rate, induced by the process, caused a large supersaturation of the aluminum matrix and the refinement of the eutectic structure. Microhardness versus time curve, performed at 250 °C, allowed to identify a stabilization of the mechanical property at a duration of 25 h. The microstructure and the mechanical properties of the samples heat treated at 25 h and at 64 h, considered as a reference for the conventionally produced alloy, were compared with the ones of the as-built alloy. Finally, it was shown that a 59% reduction of the principal residual stresses could be achieved after the 25 h-long treatment and such evolution was correlated to the mechanical behaviour.

Comparison of Stress Corrosion Cracking of High-Chromium Stainless Steels

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper NACE 2020-14695, “Comparison of Stress Corrosion Cracking Behavior of Fe13Cr5Ni- and Fe17Cr5.5Ni-Based High-Chromium Stainless Steels in High-Pressure/High-Temperature CO2 Environments,” by Yameng Qi, Zhonghua Zhang, and Chunxia Zhang, Baoshan Iron and Steel, prepared for the 2020 NACE International Corrosion Conference and Exposition, Houston, 14–18 June. The paper has not been peer reviewed. Stress corrosion cracking (SCC) of Fe13Cr5Ni- and Fe17Cr5.5Ni-based alloys in high-pressure/high-temperature (HP/HT) carbon dioxide (CO2) environments was investigated through slow-strain-rate tests (SSRTs) and electrochemical methods. The results show that a remarkable decrease in tensile strength and elongation to failure was observed when testing in a CO2 environment compared with that of air. Fe17Cr5.5Ni-based alloys possessed better SCC resistance than Fe13Cr5Ni-based alloys. The better SCC resistance of the former could be attributed to good repassivation capacity and pitting-corrosion resistance induced by the increase in chromium (Cr) and nickel (Ni) content. Introduction When service temperature exceeds 150°C, SCC resistance of Fe13Cr5Ni-based alloys could become an issue. Compared with Fe13Cr5Ni-based alloys, 22Cr duplex stainless steel has an excel-lent performance when exposed to temperatures over 150°C and stable SCC resistance in HP/HT CO2 environments. However, the cost of 22Cr duplex stainless steel is extremely high. Experimental Procedure Fe13Cr5Ni- and Fe17Cr5.5Ni-based alloys were produced by the authors’ research institute. The materials were in a quenched and tempered state. For micrographic observation, each specimen was ground with 2,000-grit carbide silicon paper and polished with 1.2-µm diamond paste. They were then degreased with acetone and etched with hydrochloric ferric chloride solution (a mixture of 5-g ferric chloride, 25-mL hydrochloric acid, and 25-mL ethanol). The steel microstructures were characterized using an optical micro-scope. The micrograph in Fig. 1a for the F-13Cr5Ni-based alloys shows a martensite phase with no notable second phases. Fe17Cr5.5Ni alloys possess long strip ferrite and martensite phases (Fig. 1b). For SSRTs, smooth tensile specimens with a gauge length of 25.4 mm and a diameter of 3.81 mm were prepared. The specimens were cut from the Fe13Cr5Ni- and Fe17Cr5.5Ni-based alloys into an 8-mm-thick, 12-mm-outer- diameter disc for electrochemical measurement. All specimens were polished to a 1,200-grit surface finish, degreased with acetone, cleansed with distilled water, and dried in air. SSRT and electrochemical-measurement procedures are detailed in the complete paper. Results SCC Susceptibility. As expected, tensile strength and elongation to failure of Fe13Cr5Ni- and Fe17Cr5.5Ni-based alloys deteriorated in HP/HT CO2 environments. Compared with an environment of air, the elongation to failure of Fe13Cr5Ni- and Fe17Cr5.5Ni-based alloys in HP/HT CO2 environments decreased by approximately 30 and 25%, respectively. In addition, tensile strength and elongation to failure of Fe17Cr5.5Ni-based alloys were greater than those of Fe13Cr5Ni-based alloys. Elongation, reduction in area, and time to failure of Fe17Cr5.5Ni-based alloys were found to be much higher than that of Fe13Cr5Ni-based alloys in HP/HT CO2 environments. It can be concluded that Fe17Cr5.5Ni alloys possess better SCC resistance than Fe13Cr5Ni alloys in these environments.

Effect of Tailored Microstructures in CaO-Added AZ31 Extrusion Material on Tensile, High Cycle Fatigue and Fatigue Crack Propagation Properties

The effect of tailored microstructures in 0.5 wt% CaO added AZ31 on tensile, high-cycle fatigue, and fatigue crack growth properties was examined. By adding CaO, the average grain size (AGS) was significantly reduced from 4.25±2.32 μm (conventional AZ31) to 2.42±1.60 μm (CaO-AZ31). The fineprecipitates of CaO-AZ31 were more evenly distributed and their fraction was higher than those of conventional AZ31. The fine-precipitates were identified as Al8Mn4Ca and (Mg, Al)2Ca in CaO-AZ31, meanwhile, were identified as Al8Mn5 and Mg17Al11 in conventional AZ31. The tensile test results showed that the yield strengths of CaO-AZ31 and conventional AZ31 were 238.0 MPa and 206.7 MPa, respectively. The elongation-to-failure also increased when CaO was added. The improved tensile properties of CaO-AZ31 could be explained by grain refinement and precipitation hardening. The high-cycle fatigue limit also increased about 15% with added CaO. The fatigue limits as a function of the tensile strengths of CaO-AZ31 and conventional AZ31 were 0.508 and 0.457, respectively. The origin of the improved fatigue resistance was attributed to inhibition of the formation of DTs, which acted as the fatigue crack source, in CaO-AZ31. In contrast, the fatigue crack growth property did not change when CaO was added. Based on the above findings, the relationships between microstructure, mechanical properties and deformation mechanisms are also discussed.

A High-Strain-Rate Superplasticity of the Al-Mg-Si-Zr-Sc Alloy with Ni Addition

The current study analyzed the effect of Ni content on the microstructure and superplastic deformation behavior of the Al-Mg-Si-Cu-based alloy doped with small additions of Sc and Zr. The superplasticity was observed in the studied alloys due to a bimodal particle size distribution. The coarse particles of eutectic origin Al3Ni and Mg2Si phases with a total volume fraction of 4.0–8.0% and a mean size of 1.4–1.6 µm provided the particles with a stimulated nucleation effect. The L12– structured nanoscale dispersoids of Sc- and Zr-bearing phase inhibited recrystallization and grain growth due to a strong Zener pinning effect. The positive effect of Ni on the superplasticity was revealed and confirmed by a high-temperature tensile test in a wide strain rate and temperature limits. In the alloy with 4 wt.% Ni, the elongation-to-failure of 350–520% was observed at 460 °C, in a strain rate range of 2 × 10−3–5 × 10−2 s−1.

Effect of Hydrogen on the Tensile Behavior of Austenitic Stainless Steels 316L Produced by Laser-Powder Bed Fusion

Hydrogen was doped in austenitic stainless steel (ASS) 316L tensile samples produced by the laser-powder bed fusion (L-PBF) technique. For this aim, an electrochemical method was conducted under a high current density of 100 mA/cm2 for three days to examine its sustainability under extreme hydrogen environments at ambient temperatures. The chemical composition of the starting powders contained a high amount of Ni, approximately 12.9 wt.%, as a strong austenite stabilizer. The tensile tests disclosed that hydrogen charging caused a minor reduction in the elongation to failure (approximately 3.5% on average) and ultimate tensile strength (UTS; approximately 2.1% on average) of the samples, using a low strain rate of 1.2 × 10−4 s−1. It was also found that an increase in the strain rate from 1.2 × 10−4 s−1 to 4.8 × 10−4 s−1 led to a reduction of approximately 3.6% on average for the elongation to failure and 1.7% on average for UTS in the pre-charged samples. No trace of martensite was detected in the X-ray diffraction (XRD) analysis of the fractured samples thanks to the high Ni content, which caused a minor reduction in UTS × uniform elongation (UE) (GPa%) after the H charging. Considerable surface tearing was observed for the pre-charged sample after the tensile deformation. Additionally, some cracks were observed to be independent of the melt pool boundaries, indicating that such boundaries cannot necessarily act as a suitable area for the crack propagation.