Research progress of residual stress measurement methods.

Residual stress refers to self-equilibrating stress present within materials, with the potential to significantly affect manufacturing processes and performance. Therefore, accurately and quantitatively measuring residual stress is always of great importance. This study provides a comprehensive review of various characterization techniques for residual stress, including their principles, development history, applications, and limitations. Initially, several destructive techniques such as the hole-drilling method, ring-core method, deep hole drilling method, slitting method, and contour method are summarized. Subsequently, three nondestructive techniques based on X-ray/electron diffraction, magnetic signals, and ultrasonic signals are evaluated. In the final part of this overview, special attention is given to a newly-developed technique for measuring residual stress, which combines incremental focused ion beam (FIB) milling and digital image correlation (DIC). Our review aims to guide further investigations on residual stress and identify the future development of techniques for measuring residual stress.

Mechanisms of Heat-Treatment-Induced Cracking in Additively Manufactured IN738 Alloy.

The present study conducts a comprehensive study on heat-treatment-induced cracking of Inconel 738 (IN738) alloy fabricated by laser powder bed fusion (LPBF) using scanning electron microscopy (SEM), energy dispersion spectrum (EDS), and electron backscatter diffraction (EBSD). The results indicate that the macroscopic crack is dominantly triggered by the strain-age cracking mechanism and propagates along grain boundaries. The initiation of cracking is facilitated by the superimposition of residual stress induced by the LPBF process and contraction stress induced by precipitation, while the reopening of compress pores at grain boundaries weakens the grain boundaries and provides fast channels for cracking. These results revealed the coupling effects in triggering heat-treatment-induced cracking, offering a fundamental guideline for crack control during heat treatment of additively manufactured IN738 alloy.

Tensile Test Coupled with an EBSD Study of a GH4169 Ring Rolled Product.

An in situ tensile test of the ring-rolled GH4169 alloy is performed to investigate the plastic deformation behavior at the micro level. Slip system activations are identified by slip traces captured by a scanning electron microscope and lattice orientation data acquired by electron backscattered diffraction. Our results demonstrated that the fraction of low-angle grain boundaries gradually increased upon tensile deformation, and the misorientation evolution in the grain interior was severely inhomogeneous. The Schmid factors at the grains of interest are calculated for comparison with the actual activated slip systems. Most of the slip system activation coincides with the Schmid law, as opposed to the initiation of other potential slip systems at some grains.

Enhanced Thermoelectric Performance of Zr1-xTaxNiSn Half-Heusler Alloys by Diagonal-Rule Doping.

Although Sb doping is regarded as the most effective method to regulate the carrier concentration within the optimum range for ZrNiSn-based half-Heusler (HH) alloys, the resulting thermal conductivity remains high. Hence, the aim of this study was to investigate the effect of "diagonal-rule" doping; that is, the Zr site was displaced by Ta, which can simultaneously enhance the electrical conductivity and reduce the lattice thermal conductivity. The solid-solubility limit of Ta in the ZrNiSn matrix was determined to be x = 0.04. The highest ZT, 0.72, was achieved at 923 K for Zr0.98Ta0.02NiSn. In addition, ZTavg increased by 10.2% for Zr0.98Ta0.02NiSn compared with that for ZrNiSn0.99Sb0.01 at 873 K, which was mainly attributed to the reduced lattice thermal conductivity of Zr0.98Ta0.02NiSn. These results suggest that Ta doping is more effective than Sb doping in ZrNiSn-based HH alloys. In addition, the microhardness of Zr1-xTaxNiSn was substantially improved with increasing Ta content and was also much higher than that of other traditional thermoelectric materials.

A nano-micro dual-scale particulate-reinforced copper matrix composite with high strength, high electrical conductivity and superior wear resistance.

Due to the contradiction between mechanical properties and electrical conductivity, it is not easy to fabricate materials with both high strength and good wear resistance with favourable electrical conductivity for the application of electrical materials. In addition, strength and wear resistance do not always present a uniform growth trend at the same time. Herein, a novel copper matrix composite reinforced by in situ synthesized ZrB2 microparticles and nano Cu5Zr precipitates is successfully prepared by a casting method and sequential heat treatments. The Cu/dual-scale particulate composite possesses a desired trade-off of strength, electrical conductivity and wear resistance. ZrB2 microparticles form from Zr and B elements in copper melts, and nanoscale Cu5Zr precipitates form in the matrix after solid solution and aging treatments. The ZrB2 microparticles, nano Cu5Zr precipitates, and well-bonded interfaces contribute to a high tensile strength of 591 MPa and superior wear resistance, with a relative electrical conductivity of 83.7% International Annealed Copper Standard.

A promising structure for fabricating high strength and high electrical conductivity copper alloys.

To address the trade-off between strength and electrical conductivity, we propose a strategy: introducing precipitated particles into a structure composed of deformation twins. A Cu-0.3%Zr alloy was designed to verify our strategy. Zirconium was dissolved into a copper matrix by solution treatment prior to cryorolling and precipitated in the form of Cu5Zr from copper matrix via a subsequent aging treatment. The microstructure evolutions of the processed samples were investigated by transmission electron microscopy and X-ray diffraction analysis, and the mechanical and physical behaviours were evaluated through tensile and electrical conductivity tests. The results demonstrated that superior tensile strength (602.04 MPa) and electrical conductivity (81.4% IACS) was achieved. This strategy provides a new route for balancing the strength and electrical conductivity of copper alloys, which can be developed for large-scale industrial application.