Superior High Strength Research Articles

Strength-ductility synergy in a non-equiatomic Co–Cr–Ni medium entropy alloy wall structure deposited using twin-wire arc additive manufacturing

An innovative twin-wire arc additive manufacturing (T-WAAM) has been deployed to fabricate a Co-rich non-equiatomic Co–Cr–Ni medium entropy alloy. The TWAAM-built single-wall structures of Co50Cr10Ni40 alloy were fabricated under argon gas shielding using dual gas metal arc welding sources. The microstructure studies revealed a single-phase FCC crystal structure and defect-free deposition. The slender columnar substructure and cellular substructure are formed along the build direction (BD) and scan direction (SD) respectively, which are commonly observed in the wall structures of other conventional FCC alloys. The tensile coupon SD and BD displayed a superior high strength and ductility combination. The T-WAAM-fabricated Co50Cr10Ni40 alloy showed both strength and elongation 1.4 times greater than that of the laser additive manufactured equiatomic CoCrNi wall structure. Thus, the study opens up a new avenue to tailor the mechanical properties of CoCrNi MEA by composition variation, with an added advantage of higher deposition rates of TWAAM.

Deep learning-enabled design for tailored mechanical properties of SLM-manufactured metallic lattice structures

The lattice structures obtained by combining repetitive light cellular forms provide superior high strength to weight capabilities compared to monolithic solid bodies. These properties of lattice structures can be further enhanced by improving the design and manufacturing process. However, the process of creating aluminum alloy lattice structures with tailored mechanical properties is still challenging due to the wide range of possible designs and their complex structure-property relationships. This paper proposes a new methodology that uses the deep learning-based 3D Generative Adversarial Network (3DGAN) model to solve this complex engineering problem. Unlike previous studies on deep learning-based lattice design, the dataset obtained through parametric design and Simulated Annealing techniques enables GAN to create new 3D lattice structures with improved mechanical strength properties. The designs generated with the GAN algorithm were produced using Selective Laser Melting Additive Manufacturing (SLM-AM) technology. The mechanical properties of SLM-fabricated (SLMed) AlSi10Mg unit cell samples were examined by a series of compression and impact tests. The results reveal that the lattice configurations generated using the generative model exhibit improved mechanical properties (e.g., a remarkable increase in normalized energy absorption and extension capacities of up to 57% and 26%, respectively). This study shows that designs generated with the 3DGAN model in lattice structures improve the design space by improving their mechanical properties. Moreover, the successful integration of deep learning and SLM-AM opens up new possibilities for creating custom parts with improved strength-to-weight ratios, dimensional accuracy, and mechanical performance.

NASA’s New Superalloy for Extreme Environments

Abstract NASA developed a novel oxide dispersion strengthened (ODS) NiCoCr-based alloy, GRX-810, that exhibits exceptional high temperature properties compared to conventional wrought superalloys for 3D printing applications. In this interview, the co-inventors, Tim Smith and Christopher Kantzos, discuss the alloy's unique development process and its superior high strength and durability for aerospace and other extreme conditions.

Heterogeneous network structures formed in TiC/TC4/β-Ti composites for enhancing strength with good ductility

Composites of TiC/(TC18 + TC4) with designed heterogeneous network structures were spark plasma sintered using reinforcement precursors of graphene and β-TC18 alloy to reinforce TC4 matrix. The heterogeneous networks of TiC/(TC18 + TC4) composites are typically mixed microstructures of α+β lamellar and equiaxed β phases. The synthesized composites exhibit superior high strength and ductility (i.e., with a fracture strength of 1150 MPa and a uniform elongation of 5%), compared with those of the sintered monolithic TC4 (900 MPa-10%) and TC18 (1330 MPa-1.7%). Incompatible plastic deformation behaviors of TC18 and TC4 enhance strain hardening effect, which is the main reason for the enhanced ductility of the composites. Refinement strengthening and heterostructure-deformation induced hardening are two key mechanisms to achieve the high strength. This study provides a new strategy to simultaneously enhance strength and ductility for Ti matrix composites.

A Superior High-Strength Dilute Mg-Bi-Ca Extrusion Alloy with a Bimodal Microstructure

Improving the mechanical properties of Mg alloys is of great significance for their wide application. A micro-alloyed Mg-1.45Bi-0.79Ca alloy (in wt.%) exhibiting a high tensile yield strength of 394 ± 5 MPa and a moderate elongation of 6.6 ± 0.6% was fabricated by single pass extrusion. The superior high strength is mainly attributed to the synergy effects of ultra-fine dynamic recrystallized grains; numerous Mg2Ca, Mg3Bi2, and Mg2Bi2Ca nano-precipitates; residual dislocations; sub-grain boundaries; as well as strong <10-10> fibre texture in the extrusion direction.

Recrystallisation behaviour and mechanical properties of a novel Re-containing nickel-base superalloy

ABSTRACTA newly developed heavily alloyed polycrystalline nickel-base superalloy containing rhenium and intended as a structural material for turbine discs in gas turbine engines has been studied. Homogenisation and heterogenisation heat treatments were developed for the as-cast superalloy, which led to improving the hot workability as compared to that of as-cast material. electron backscatter diffraction analysis of samples isothermally compressed at temperatures near the solvus temperature showed that continuous dynamic recrystallisation occurred in the superalloy leading to the formation of refined recrystallised structure. These results were used for the development of canned forging processing under quasi-isothermal conditions. The superalloy subjected to canned forging followed by aging exhibited superior high strength and high-temperature capability, while retaining reasonable ductility as compared to known disc superalloys.

Excellent mechanical properties obtained by low temperature extrusion based on Mg-2Zn-1Al alloy

A newly developed low Al containing magnesium alloy, Mg-2Zn-1Al based alloy (wt.%) shows excellent mechanical properties. The alloys with superior high strength and considerable ductility (the maximum of tensile strength reaches 332 MPa and corresponding elongation is 23.1%) were produced by electromagnetic casting and extrusion at relatively low temperatures (110 °C, 170 °C, 210 °C, and 250 °C) with an extrusion ratio of 17.4:1. Effects of extrusion temperature on the evolution of microstructure, mechanical properties and extruded texture were investigated by OM, SEM, TEM, and EBSD analysis. The microstructures of the alloy extruded at low temperatures mainly consist of the equiaxed dynamically recrystallized grains, elongated grains, and regions without dynamic recrystallization. And there are only equiaxed dynamically recrystallized grains in the alloy extruded at 250 °C. The increasing extrusion temperature results in grain coarsening and strength reduction. When the extrusion temperatures are 110 °C and 170 °C, the average grain size reaches submicron level of 0.65 μm and 0.89μm, respectively. Because the higher extrusion temperature makes the dynamically recrystallized grains rotate in a favorable direction, the basal texture enhances with the rise of extrusion temperature. The high strength is mainly attributed to the structure of extremely refined grains. High ductility benefits from a large amount of basal slip, activation of non-basal slip, and grain boundary movement under the action of tensile stress.

Microstructure and mechanical properties of a novel polycrystalline rhenium-containing nickel-based disc superalloy subjected to hot forging

A newly developed heavy alloyed polycrystalline nickel-based superalloy SDZhS-15 containing rhenium and intended as a structural material for turbine discs in gas turbine engines has been studied. Multiple homogenization and heterogenization heat treatment was developed for the superalloy to improve its hot workability. The heat treated workpieces were subjected to single-step hot forging under quasi-isothermal conditions at temperatures slightly below the γ′ solvus temperature followed by air cooling and ageing. As a result, sound forgings with an inhomogeneous, partially recrystallized microstructure were produced. The obtained forgings were used for preparation of specimens for mechanical testing. The new superalloy showed superior high strength and high temperature capability, while retaining reasonable ductility in comparison with currently known disc superalloys.

Effect of extrusion temperature on the microstructure and mechanical properties of low Zn containing wrought Mg alloy micro-alloying with Mn and La-rich misch metal

A new low Zn containing Mg-1.5Zn-0.4Mn-0.9LaMM (La-rich misch metal) alloy with excellent mechanical properties is developed. The alloys with superior high strength and respectable ductility (the maximum of UTS reaches 353 MPa and corresponding EL 19.4%) are fabricated by mold casting and indirect extrusion. Effects of extrusion temperature on the evolution of microstructure, mechanical properties and extruded texture are investigated by SEM, XRD and TEM analysis. The addition of LaMM is found to produce typical bimodal structure of fine DRXed (dynamic recrystallized) grains and elongated un-DRXed grains when extruded at relatively low temperature. The relatively high strength is primarily due to the grain boundary strengthening and precipitation strengthening, moreover the large hard elongated deformed grains functioning as in-situ strength-reinforcement fibers also apparently contribute to the strength improvement. The equixal, refined DRXed grain structure and comparable different extruded texture component with traditional AZ31 and other alloys with similar microstructure are believed to enhance its ductility.

Multimodal Microstructure and Mechanical Properties of AZ91 Mg Alloy Prepared by Equal Channel Angular Pressing plus Aging

Developing cost-effective magnesium alloys with high strength and good ductility is a long-standing challenge for lightweight metals. Here we present a multimodal grain structured AZ91 Mg alloy with both high strength and good ductility, prepared through a combined processing route of low-pass ECAP with short-time aging. This multimodal grain structure consisted of coarse grains and fine grains modified by heterogeneous precipitates, which resulted from incomplete dynamic recrystallization. This novel microstructure manifested in both superior high strength (tensile strength of 360 MPa) and good ductility (elongation of 21.2%). The high strength was mainly attributed to the synergistic effect of grain refinement, back-stress strengthening, and precipitation strengthening. The favorable ductility, meanwhile, was ascribed to the grain refinement and multimodal grain structure. We believe that our microstructure control strategy could be applicable to magnesium alloys which exhibit obvious precipitation strengthening potential.

Hysteresis modeling of sequential application of orthogonal fields

In a cumulative effort to characterize the sizes, shapes, and distributions of the domains of the structurally superior high strength steels, a characteristic magnetization measurement and a Preisach model are presented to explain and model the distinctive trends observed in the data. The study investigates the effect of a constant transverse magnetic field and a cycling longitudinal magnetic field, applied sequentially, on the major hysteresis loop of solid cylinders of high strength steel. A coupled-hysteron vector Preisach model is extended to model the longitudinal magnetization of the samples under the effect of an applied transverse field. Insights about the microstructure of the rods and the contribution of different domains and magnetization mechanisms to the magnetic response are drawn.

On the origin of superior high strength of Ti–45Al–10Nb alloys

The yield strengths of Ti–45Al–10Nb alloys with a near-gamma (NG) microstructure were measured at temperatures up to 900 °C. The NG Ti–45Al–10Nb alloys exhibited significantly higher yield strengths than conventional TiAl-base alloys with comparable microstructure. These high strengths appear to arise from the solid-solution hardening of Nb additions as concluded by comparing the friction stresses for TiAl alloys with and without Nb addition. The hardening effect of Nb additions was found to be dependent on the Al content of γ phase, being less significant in the γ phase containing higher aluminum. The origin of this dependence is postulated to be the varying site occupation of Nb in γ phase with different Al concentrations.