High-entropy alloys (HEAs) are alloys with five or more principal elements. Due to the distinct design concept, these alloys often exhibit unusual properties. Thus, there has been significant interest in these materials, leading to an emerging yet exciting new field. This paper briefly reviews some critical aspects of HEAs, including core effects, phases and crystal structures, mechanical properties, high-temperature properties, structural stabilities, and corrosion behaviors. Current challenges and important future directions are also pointed out.

https://www.tandfonline.com/doi/pdf/10.1080/21663831.2014.912690

High-Entropy Alloys: A Critical Review

https://ir.nctu.edu.tw:443/bitstream/11536/8537/1/000258250100017.pdf

Integrating the Kano model into a robust design approach to enhance customer satisfaction with product design

A multi-response optimization problem has been developed in search of an optimal parametric combination to yield favorable bead geometry of submerged arc bead-on-plate weldment. Taguchi’s L25 orthogonal array (OA) design and the concept of signal-to-noise ratio (S/N ratio) have been used to derive objective functions to be optimized within experimental domain. The objective functions have been selected in relation to parameters of bead geometry viz. bead width, bead reinforcement, depth of penetration and depth of HAZ. The Taguchi approach followed by Grey relational analysis has been applied to solve this multi-response optimization problem. The significance of the factors on overall output feature of the weldment has also been evaluated quantitatively by analysis of variance method (ANOVA). Optimal result has been verified through additional experiment. This indicates application feasibility of the Grey-based Taguchi technique for continuous improvement in product quality in manufacturing industry.

Grey-based taguchi method for optimization of bead geometry in submerged arc bead-on-plate welding

The Mg/Al laminated composite was fabricated by the accumulative roll bonding (ARB) using the pure magnesium and Al5052 alloy at 400 °C. Tensile properties along rolling direction and the transverse direction and the microhardness were evaluated at the ambient temperature. The tensile strength of the laminated Mg/Al composite along both directions increased gradually till two ARB cycles, but then decreased after the third ARB cycles. Optical microscopy and scanning electron microscopy (SEM) were utilized to reveal the microstructure evolution and the failure mechanism. Grain refinement of Mg layers was not obvious during the ARB process due to the high temperature and interval reheating. The obvious crack at the coarse intermetallic compounds and rupture of the Al layer after the third cycle led to the premature failure of the sample along the rolling direction during the tensile test.

Microstructure and mechanical properties of the Mg/Al laminated composite fabricated by accumulative roll bonding (ARB)

In the present work, CO 2 continuous laser welding process was successfully applied and optimized for joining a dissimilar AISI 316 stainless-steel and AISI 1009 low carbon steel plates. Laser power, welding speed and defocusing distance combinations were carefully selected with the objective of producing welded joint with complete penetration, minimum fusion zone size and acceptable welding profile. Fusion zone area and shape of dissimilar austenitic stainless-steel with ferritic low carbon steel were evaluated as a function of the selected laser welding parameters. Taguchi approach was used as statistical design of experiment (DOE) technique for optimizing the selected welding parameters in terms of minimizing the fusion zone. Mathematical models were developed to describe the influence of the selected parameters on the fusion zone area and shape, to predict its value within the limits of the variables being studied. The result indicates that the developed models can predict the responses satisfactorily.

Using Taguchi method to optimize welding pool of dissimilar laser-welded components

The use of grey-based Taguchi methods to determine submerged arc welding process parameters in hardfacing

A series of high chromium Fe–Cr–C hardfacing alloys were produced by gas tungsten arc welding (GTAW). Chromium and graphite alloy fillers were used to deposit coatings on ASTM A36 steel substrates. These coatings were especially designed to vary the size and proportion of the (Cr,Fe)23C6 carbides that are present in the microstructure at room temperature. Depending on the three different graphite additions of those alloy fillers, hypoeutectic, eutectic and hypereutectic microstructures were obtained on coated surfaces. No crack formation was found on the coatings. According to the X-ray diffraction analysis and microstructure characteristics, the hypereutectic composites consist of three phases, i.e. Cr–Fe solid solution (α), (Cr,Fe)23C6 and trace amounts of (Cr,Fe)7C3. Massive (Cr,Fe)23C6 contain (Cr,Fe)7C3 in the center, and cause its high hardness value up to HRC 70. And the massive (Cr,Fe)23C6 are surrounded by a eutectic structure to restrain cracks from appearing. All the microstructure constituents were rationalized in terms of a ternary diagram.

Microstructure change caused by (Cr,Fe)23C6 carbides in high chromium Fe–Cr–C hardfacing alloys

Microstructural and abrasive characteristics of high carbon Fe-Cr-C hardfacing alloy

The current study used flux core arc welding to produce a series of hypereutectic Fe–Cr–C claddings with various carbon content. Depending on the carbon content, this research produced hypereutectic microstructures of γ-Fe + (Cr,Fe)7C3 carbides. As the carbon content of a cladding increased from 3.73 to 4.85 wt.%, the surface fractions of carbides increased from 33.8% to 86.1%. The morphology of primary (Cr,Fe)7C3 carbides also transited from a blade-like to a rod-like shape. With regard to wear performance, the relationship between wear resistance and hardness (H) is non-linear. However, the mean free path (λ) of primary (Cr,Fe)7C3 carbides must be considered. Wear resistance is proportional to H/λ. The primary carbides can prevent the eutectic colonies from selective abrasion. The rod-like (Cr,Fe)7C3 carbides also provide much better wear resistance because rod-like carbides have a greater hardness. After an abrasive wear process, abrasive particles cause plastic plows when the cladding has lower surface fractions of carbides. The fracture of primary carbides leads into the craters where it occurs in the worn cladding surface with higher surface fractions of carbides.

Chia-Ming Chang

Papers

The use of grey-based Taguchi methods to determine submerged arc welding process parameters in hardfacing

Microstructure change caused by (Cr,Fe)23C6 carbides in high chromium Fe–Cr–C hardfacing alloys

Microstructural and abrasive characteristics of high carbon Fe-Cr-C hardfacing alloy

Microstructure and wear characteristics of hypereutectic Fe–Cr–C cladding with various carbon contents

Micro-structural characteristics of Fe–40 wt%Cr–xC hardfacing alloys with [1.0–4.0 wt%] carbon content