Delineating the Ultra-Low Misorientation between the Dislocation Cellular Structures in Additively Manufactured 316L Stainless Steel.

Sub-micro dislocation cellular structures formed during rapid solidification break the strength-ductility trade-off in laser powder bed fusion (LPBF)-processed 316L stainless steel through high-density dislocations and segregated elements or precipitates at the cellular boundaries. The high-density dislocation entangled at the cellular boundary accommodates solidification strains among the cellular structures and cooling stresses through elastoplastic deformation. Columnar grains with cellular structures typically form along the direction of thermal flux.

Martensitic Phase-Transforming Metamaterial: Concept and Model.

We successfully developed a mechanical metamaterial that displays martensitic transformation for the first time. This metamaterial has a bistable structure capable of transitioning between two stable configurations through shear deformation. The outer shape of the unit cell of this structure is a parallelogram, with its upper and lower sides forming the bases of two solid triangles.

Big-Volume SliceGAN for Improving a Synthetic 3D Microstructure Image of Additive-Manufactured TYPE 316L Steel.

A modified SliceGAN architecture was proposed to generate a high-quality synthetic three-dimensional (3D) microstructure image of TYPE 316L material manufactured through additive methods. The quality of the resulting 3D image was evaluated using an auto-correlation function, and it was discovered that maintaining a high resolution while doubling the training image size was crucial in creating a more realistic synthetic 3D image. To meet this requirement, modified 3D image generator and critic architecture was developed within the SliceGAN framework.

Effect of Rapid Heating and Cooling Conditions on Microstructure Formation in Powder Bed Fusion of Al-Si Hypoeutectic Alloy: A Phase-Field Study.

Al alloy parts fabricated by powder bed fusion (PBF) have attracted much attention because of the degrees of freedom in both shapes and mechanical properties. We previously reported that the Si regions in Al-Si alloy that remain after the rapid remelting process in PBF act as intrinsic heterogeneous nucleation sites during the subsequent resolidification. This suggests that the Si particles are crucial for a novel grain refinement strategy.

Effects of carbon addition on wear mechanisms of CoCrMo metal-on-metal hip joint bearings.

The wear behaviors of biomedical CoCrMo prosthetic alloys containing various amounts of carbon were investigated using a standard hip joint simulator in a simulated body fluid. A few chunks and punctate σ-phase precipitates were observed in the low-carbon (LC) alloy; these were responsible for the abrasion and run-in wear. Increasing the carbon content led to greater precipitation of globular MC-type carbides.

Effects of surface friction treatment on the in vitro release of constituent metals from the biomedical Co-29Cr-6Mo-0.16N alloy.

Due to the ignorance by many researchers on the influence of starting microstructure on the metal release of biomedical materials in human body after implant, in this study, the effect of surface friction treatment on the in vitro release of the constituent elements of the biomedical Co-29Cr-6Mo-0.16N (CCM) alloy is investigated for the first time by immersion test in lactic acid solution combined with electron backscatter diffraction, transmission electron microscope, X-ray diffraction, X-ray photoelectron spectroscopy, and inductively coupled plasma atomic emission spectroscopy (ICP-EOS). The results indicate that friction treatment on the as-annealed CCM alloy sample surface leads to a planar strain-induced martensitic transformation (SIMT) on sample surface; this greatly accelerates the release of all the constituent elements and, in particular, that of Co as indicated by the ICP-EOS analysis.

Uneven damage on head and liner contact surfaces of a retrieved Co-Cr-based metal-on-metal hip joint bearing: An important reason for the high failure rate.

Detailed metallurgical investigations have been performed on a used Co-Cr-based metal-on-metal (MoM) hip joint bearing containing a type of liner that is commonly used in such joints. The damage on the metal-liner sliding surface was considerably more severe than that on the metal head counterpart, in terms of wear-scar density and width and microcrack frequency. Cross-sectional transmission electron microscopy revealed that a thick (>3 μm) nanocrystalline layer formed on the sliding surface of the head, whereas the liner had coarse carbides embedded in it and nanocrystals were formed in a very limited region no deeper than 1 μm.

Quantitative in vivo biocompatibility of new ultralow-nickel cobalt-chromium-molybdenum alloys.

Nickel (Ni) eluted from metallic biomaterials is widely accepted as a major cause of allergies and inflammation. To improve the safety of cobalt-chromium-molybdenum (Co-Cr-Mo) alloy implants, new ultralow-Ni Co-Cr-Mo alloys with and without zirconium (Zr) have been developed, with Ni contents of less than 0.01%.

Detwining in Mg alloy with a high density of twin boundaries.

To investigate the role of preexisting twin boundaries in magnesium alloys during the deformation process, a large number of {10-12} tensile twins were introduced by a radial compression at room temperature before hot compressive tests with both low and high strain rates. Unlike the stable twins in Cu-based alloys with low stacking fault energies, {10-12} twins in Mg alloy are extremely unstable or easy to detwin through {10-12}-{10-12} re-twinning. As a result, non-lenticular residual twins and twin traces with misorientation of 5°-7° were present, as confirmed by electron backscatter diffraction.

Local strain evolution due to athermal γ→ε martensitic transformation in biomedical CoCrMo alloys.

Locally developed strains caused by athermal γ face-centered cubic (fcc)→ε hexagonal close-packed (hcp) martensitic transformation were investigated for the γ matrix of Ni-free Co-29Cr-6Mo (wt%) alloys prepared with or without added nitrogen. Electron-backscatter-diffraction-(EBSD)-based strain analysis revealed that in addition to ε-martensite interiors, the N-free alloy that had a duplex microstructure consisting of the γ matrix and athermal ε-martensite plates showed larger magnitudes of both elastic and plastic strains in the γ phase matrix than the N-doped counterpart that did not have a ε-martensite phase. Transmission electron microscopy (TEM) results indicated that the ε-martensite microplates were aggregates of thin ε-layers, which were formed by three different {111}γ〈112¯〉γ Shockley partial dislocations in accordance with a previously proposed mechanism (Putaux and Chevalier, 1996) that canceled the shear strains of the individual variants.

Copper-catalyzed synthesis of esters from ketones. Alkyl group as a leaving group.

The conversion of ketones to esters has been achieved through the use of Cu catalyst and tetrabutylammonium nitrite. This reaction involves the activation of the less activated C-C bond, and the alkyl group is removed as a leaving group. Various isopropyl ketones are found to be good substrates for this reaction.