Tsung-Shune Chin

Bio: Tsung-Shune Chin is an academic researcher from National Tsing Hua University. The author has contributed to research in topics: Microstructure & Crystallite. The author has an hindex of 3, co-authored 3 publications receiving 5702 citations. Previous affiliations of Tsung-Shune Chin include National United University.

Nanostructured High-Entropy Alloys with Multiple Principal Elements: Novel Alloy Design Concepts and Outcomes

Abstract: A new approach for the design of alloys is presented in this study. These high-entropy alloys with multi-principal elements were synthesized using well-developed processing technologies. Preliminary results demonstrate examples of the alloys with simple crystal structures, nanostructures, and promising mechanical properties. This approach may be opening a new era in materials science and engineering.

Formation of simple crystal structures in Cu-Co-Ni-Cr-Al-Fe-Ti-V alloys with multiprincipal metallic elements

Abstract: Crystalline solid solutions are typically formed in conventional alloys based on one or two host elements. Here, in this research, four alloys containing multiprincipal metallic elements (≥5 elements) were prepared by casting, splat quenching, and sputtering. Their microstructures and crystal structures were investigated. It was interestingly found that solid solutions with simple fcc or bcc crystal structure were also practically formed in these alloys with multiprincipal elements. All different atoms are regarded as solutes and expected to randomly distribute in the crystal lattices without any matrix element defined.

Residual stress analysis of electrodeposited thick CoMnP monolayers and CoMnP/Cu multilayers

Abstract: Residual stress in electroplated hard magnetic layers is crucial to the stability and durability in end applications. We electrodeposited highly HCP (002) textured CoMnP hard magnetic layers on copper substrate. We characterized and compared the residual stresses of mono- and multi-layered configurations using sin2ψ X-ray diffraction (XRD) for the apparent crystallite stress (σXRD), and curvature measurement methods for the macro-stress (σf). Intermediate Cu layer having a fixed thickness of 1.4 μm was introduced as a stress reliever for the multilayered CoMnP/Cu through sequential electrodeposition. In multilayers, thickness of all single magnetic layers was added to around ~20 μm similar to that of a monolayer. The surface morphology, layer composition and microstructure remain the same regardless of individual CoMnP single layer thickness. XRD results of ϕ-scan and ψ-scan depict the transversely isotropic CoMnP layers are under an equi-biaxial stress status, making a simplified analytical solution of sin2ψ method. The residual stresses measured by XRD sin2ψ method have been correlated with those acquired by curvature method. Increasing the number of layers from 2, 3 to 6 in the CoMnP/Cu multilayers reduces the σXRD by 8.3%, 25%, 33%, respectively; while the σf by 7.7%, 15% and 23%, respectively, as compared to those of the CoMnP mono-layer. These reductions are attributed to the released strain energy due to soft interlayer confinement and stacking fault formation. Elaborated includes unambiguous understandings of residual stress and microstructures for the electrodeposited CoMnP layers.

Microstructure and thermal diffusivity investigations of RF-sputtered tantalum nitride films

Abstract: Tantalum nitride films were prepared by RF magnetron sputtering. The thermal diffusivity of these films was measured using a traveling thermal wave method. The measured values of thermal diffusivity are within the range 0.10–0.15 cm2/s with a deviation ±0.01 cm2/s and proportional to the nitrogen contents. The incorporation of oxygen impurity in the TaN films was found not available as examined by transmission electron microscopy (TEM) and X-ray photoelectron spetroscopy (XPS) quantitative analyses. TEM examination shows that the microstructure in TaN film, deposited with an N2/Ar flow ratio 1:19, is composed of metallic particles dispersed in an amorphous matrix. High resolution TEM photograph reveals that the amorphous structure further contains a nano-crystalline phase embedded in a continuous amorphous phase. The nano-crystalline particles are characterized as hexagonal Ta2N phase with a lattice spacing d110=3.05 A. By XPS Ta(4f) spectra, some Ta–N and Ta–O signals were evidenced to co-exist in a broadened peak. Furthermore, by FTIR analysis, a new vibration not reported before in the literature was found at 1118 cm-1 that has been assigned to the Ta–N–O linkage in the films.

Residual stress tuned magnetic properties of thick CoMnP/Cu multilayers

Abstract: Electrodeposited hard magnetic thick films have vast applications in the microelectromechanical systems (MEMS). Yet the very large residual stresses (σr) built-up in monolayered thick magnetic films leads to cracks, dimensional changes and deteriorated magnetic properties. Here, we explored quantitatively magnetic properties of CoMnP/Cu multilayers tuned by σr, which in turn are varied by the inserted soft Cu interlayer and thickness of single CoMnP magnetic layers. The configuration of the multilayers is an alternating CoMnP/Cu on Cu-substrate. The thickness of Cu interlayer was 1.4 μm. We kept a sum of all magnetic layers in the multilayers at ∼20 μm to benchmark with a 19.4 μm monolayered CoMnP. The magnetic layers are 94 wt.% Co and possess highly textured (002) hexagonal close packed microstructures. We characterized the apparent crystallite stresses through sin2ψ method by X-ray diffractometer (XRD) and residual film stress by curvature method. The insertion of Cu interlayers effectively reduces σr by 23% through stacking with six single-layered CoMnP. The out-of-plane (OP) anisotropy is slightly reduced. While the maximum energy product in the in-plane (IP) direction can be significantly enhanced by 430% ∼ 690% with increasing the number of the CoMnP single layer in the multilayers. The magneto-elastic behaviors well explain the evolution of the total anisotropy energy of the mono- and multi-layers. By CoMnP/Cu configurations we successfully worked out a strategy to preserve prestigious OP performance while to enhance IP properties by 4 to 6 times to meet ever increasing challenges in MEMS applications.

A fracture-resistant high-entropy alloy for cryogenic applications

Abstract: High-entropy alloys are equiatomic, multi-element systems that can crystallize as a single phase, despite containing multiple elements with different crystal structures. A rationale for this is that the configurational entropy contribution to the total free energy in alloys with five or more major elements may stabilize the solid-solution state relative to multiphase microstructures. We examined a five-element high-entropy alloy, CrMnFeCoNi, which forms a single-phase face-centered cubic solid solution, and found it to have exceptional damage tolerance with tensile strengths above 1 GPa and fracture toughness values exceeding 200 MPa·m(1/2). Furthermore, its mechanical properties actually improve at cryogenic temperatures; we attribute this to a transition from planar-slip dislocation activity at room temperature to deformation by mechanical nanotwinning with decreasing temperature, which results in continuous steady strain hardening.

Metastable high-entropy dual-phase alloys overcome the strength–ductility trade-off

Abstract: Metals have been mankind's most essential materials for thousands of years; however, their use is affected by ecological and economical concerns Alloys with higher strength and ductility could alleviate some of these concerns by reducing weight and improving energy efficiency However, most metallurgical mechanisms for increasing strength lead to ductility loss, an effect referred to as the strength-ductility trade-off Here we present a metastability-engineering strategy in which we design nanostructured, bulk high-entropy alloys with multiple compositionally equivalent high-entropy phases High-entropy alloys were originally proposed to benefit from phase stabilization through entropy maximization Yet here, motivated by recent work that relaxes the strict restrictions on high-entropy alloy compositions by demonstrating the weakness of this connection, the concept is overturned We decrease phase stability to achieve two key benefits: interface hardening due to a dual-phase microstructure (resulting from reduced thermal stability of the high-temperature phase); and transformation-induced hardening (resulting from the reduced mechanical stability of the room-temperature phase) This combines the best of two worlds: extensive hardening due to the decreased phase stability known from advanced steels and massive solid-solution strengthening of high-entropy alloys In our transformation-induced plasticity-assisted, dual-phase high-entropy alloy (TRIP-DP-HEA), these two contributions lead respectively to enhanced trans-grain and inter-grain slip resistance, and hence, increased strength Moreover, the increased strain hardening capacity that is enabled by dislocation hardening of the stable phase and transformation-induced hardening of the metastable phase produces increased ductility This combined increase in strength and ductility distinguishes the TRIP-DP-HEA alloy from other recently developed structural materials This metastability-engineering strategy should thus usefully guide design in the near-infinite compositional space of high-entropy alloys