Hexagonal Close-Packed Metals and Alloys: Processing, Microstructure and Properties

Editorial

15 March 2021

Editorial: Hexagonal Close-Packed Metals and Alloys: Processing, Microstructure and Properties

Liang-Yu Chen

Linjiang Chai

and

Lai-Chang Zhang

1,960 views

2 citations

Editors

Liang-Yu Chen

Jiangsu University of Science and Technology

Lai-Chang Zhang

Edith Cowan University

Linjiang Chai

Chongqing University of Technology

Impact

(a) Schematic image of MAO coating roughness measured by five lines; (b) roughness of MAO coatings under different current modes.

Original Research

18 September 2020

Properties of Micro-Arc Oxidation Coating Fabricated on Magnesium Under Two Steps Current-Decreasing Mode

Ze-Xin Wang

, 5 more and

Xi-Zhi Jiang

A concept of two-steps current-decreasing mode derived from constant current mode was developed to fabricate micro-arc oxidation (MAO) coatings on ZK60 magnesium alloy in a dual electrolyte system. The growth characteristics of coatings were analyzed by voltage-time curves, and the coating microstructures were characterized by means of scanning electron microscopy. Meanwhile, the roughness, corrosion behavior, and microhardness of MAO coatings were investigated. The results show that the MAO coatings exhibit a smooth and compact surface, and have improved hardness, higher thickness, smaller roughness, and uneven distribution of holes. Such positive characteristics result in improved corrosion resistance of MAO coatings. The coating produced under the two-steps current mode of “1.2–0.6A” shows a smaller corrosion rate of 0.1559 g/m²⋅h compared with the one produced under the other mode. The results of nanoscratch tests show that the coating fabricated by “1.2–0.6 A” mode has strong bond strength with the substrate. Under this optimized mode, the MAO process also has the lowest energy consumption of 49.8 W/(dm²⋅μm).

5,202 views

22 citations

Original Research

28 August 2020

The Effect of Cold Swaging Deformation on the Microstructures and Mechanical Properties of a Novel Metastable β Type Ti–10Mo–6Zr–4Sn–3Nb Alloy for Biomedical Devices

Jun Cheng

, 8 more and

Zhentao Yu

$TEM BF images and SAD patterns of the Ti–10Mo–6Zr–4Sn–3Nb alloy cold swaged with reductions of: (A) 25%, (B) 55%, and (C) 75%, (D) Schematic diagram of the Burgers relationship between stress-induced martensite and the β matrix (BF: Bright Field; SAD: Selected Area Diffraction).$

This work investigated the microstructures, texture evolution, and mechanical properties of newly designed metastable β type Ti–10Mo–6Zr–4Sn–3Nb (wt.%) alloys for biomedical devices, which were subjected to cold swaging deformation with reductions of 15–75%. With the increment in the reduction of swaging deformation, the grains are broken and gradually refined, and stress-induced martensite transformation takes place, resulting in the formation of the α” phase. Moreover, the {1 1 2} <1 1 1> and {1 1 0} <1 1 2> fibers turn into γ-fiber {1 1 1} <1 1 0> and α-fiber {1 1 2} <1 1 0> with the increment in the swaging reduction. The α-fiber texture in particular, first weakens and then strengthens during cold deformation. Under the combined effect of sub-structures, grain refinement, and texture evolution, the strength of the alloy is gradually enhanced with the increment in the cold deformation reduction. The solution-treated alloy bar shows superior cold workability in the swaging process. The plasticity remains at a moderate level because the initial grains have not been completely broken at the beginning of cold swaging deformation. The elastic modulus of the alloy shows a downward trend with an increasing reduction, which is related to the dislocation multiplication, grain refinement, and grain orientation evolution during cold swaging deformation.

2,345 views

16 citations

EM-EDS mapping shows (a) the ZrO2 particles embedded in matrix (b–f) color mapping of elements O, Mg, Al, Zn, and Zr of the SZ-center in FSPed AZ31/ZrO2 composite (Z3-3P Specimen).

Original Research

14 August 2020

Microstructure and Mechanical Properties of AZ31/ZrO2 Composites Prepared by Friction Stir Processing With High Rotation Speed

Qianhao Zang

, 6 more and

Sheng Lu

2,690 views

11 citations

Original Research

07 July 2020

Preparation and Degradation Behavior of Composite Bio-Coating on ZK60 Magnesium Alloy Using Combined Micro-Arc Oxidation and Electrophoresis Deposition

Ze-Xin Wang

, 6 more and

Jun Yang

In this work, ZK60 magnesium alloy was employed as the substrate substratum for producing micro-arc oxidation (MAO) coating which contains Ca and P. Electrophoretic deposition (ED) process was conducted on the micro-arc oxidized sample to prepare a hydroxyapatite (HA) layer on the original coating. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and Fourier transform infrared spectroscopy (FT-IR) were used to analyze the phase constituents and microstructures of both MAO and MAO-ED coatings. Corrosion resistance and degradation behavior of the coatings in SBF were investigated by electrochemical tests and simulated body fluid (SBF) immersion tests. The results indicate that a dense HA layer about 5 μm in thickness had been successfully prepared on the MAO coating. After going through the ED process, the porosity of the MAO-ED coating had decreased from 5.63 to 0.81%. The Ca/P ratio of the MAO-ED coating had become 1.60, which indicates a potential biocompatibility of the material. Therefore, the MAO-ED coating can induce the deposition of bioactive products from SBF. During an immersion test of SBF for 10 days, the weight gain of MAO-ED sample continued to increase, showing that the deposition rate of the induced products is always higher than that of corrosion products before experiencing the 10 days of immersion. The deposition of induced products protects the substrate from being corroded so effectively that it ensures the good mechanical properties and biocompatibility during the initial stage of implantation. According to the changes in sample morphologies and the electrochemical measurements in SBF, a relevant degradation model has been suggested and the underlying mechanism for degradation behavior is discussed.

3,584 views

15 citations