Band 112, Heft 7

In this paper the hot working behaviour of medium carbon duplex cast steel is studied using uniaxial hot compression tests over a temperature range varying from 700 ˚C to 1 000 °C and at different strain rates ranging from 10– 4 to 10 –1 s –1 . A model based on a variant of a dynamic materials model was employed to construct processing maps. These maps delineate the safe and unsafe domains. The safe domains, associated with dynamic recrystallization and dynamic recovery, can be chosen to optimize the hot workability of the studied material. Whereas, the unsafe domain is to be avoided because it is associated with plastic deformation instabilities. The domain associated with dynamic recrystallization is centred at 1000 °C and 10 –4 s –1 with a peak energy dissipation efficiency of about 40%, while the domain associated with dynamic recovery is centred at 700 °C and 10 –4 s –1 with a peak energy dissipation efficiency of about 27%. The unsafe hot working domain, spread over the entire temperature range and moderate to high strain rates, predicts the appearance of flow instabilities, in the form of shear bands and intergranular cracks. To validate the obtained results, microstructural observations corresponding to different processing conditions are presented.

An Nd:YAG laser device is used to conduct laser welding for a 1 mm austenitic stainless steel plate and a ferritic stainless steel plate. A finite element model of the shear punching test is constructed to generate the maximum shear strength in the weld, and the finite element model of laser welding is created using the welding temperature field. The hole drilling test result and the residual stress generated by two algorithms (Nonuniform-material and uniform-material) are compared. Results show that a drop-off of residual stress in the central area of the welded joint is observed when materials heterogeneity is disregarded. When materials heterogeneity is considered, the residual stress curve indicates smooth transition. The value of the latter appears reasonably similar to the experimental value. Therefore, this solution is advantageous in terms of residual stress simulation in dissimilar welded joints and does not critically affect residual deformation.

AlCrFeCoNi particles were added to Mg-9Al-1Zn alloy in a rotary blowing process. The microstructures and mechanical properties of Mg-9Al-1Zn based composites were characterized by means of X-ray diffraction, optical microscopy, scanning electron microscopy, transmission electron microscopy, and tensile and compression tests at room temperature. Results revealed that AlCrFeCoNi particles could effectively refine the grains, and the rotary blowing process enabled the uniform distribution of these particles. The mechanical properties of composites improved with the increase of particle volume fraction. The superior wettability of AlCrFeCoNi particles supported their reliable bonding with the Mg-9Al-1Zn matrix. The Hall–Petch strengthening and stress transfer effect played a dominant role in the improvement of compressive and tensile properties.

The present work cast a complex Mg-6Gd-3Y-0.5Zr alloy component in a polybenzylic ether phenolic resin (PEP-SET) sand mold using by differential pressure casting. Microstructural characterization was carried out on the castings in the states of as-cast, solution treatment and aging treatment. Their mechanical properties were examined at elevated temperatures. The studied Mg alloy showed noticeably high tensile strengths up to 473 K, followed by a significant decrease with further increasing the testing temperatures. Its mechanical properties at elevated temperatures were compared with those of WE43 alloy fabricated under identical casting conditions.

The most promising metal processing additive manufacturing technique in industry is selective laser melting, but only a few alloys are commercially available, limiting the potential of this technique. In particular high strength aluminum alloys, which are of great importance in the automotive industry, are missing. An aluminum 2024 alloy, reinforced by Ti-6Al-4V and B 4 C particles, could be used as a high strength alternative for aluminum alloys. Heat treating can be used to improve the mechanical properties of the metal matrix composite. Dynamic scanning calorimetry shows the formation of Al 2 Cu precipitates in the matrix instead of the expected Al 2 CuMg phases due to the loss of magnesium during printing, and precipitation processes are accelerated due to particle reinforcement and additive manufacturing. Strong reactions between aluminum and Ti-6Al-4V are observed in the microstructure, while B 4 C shows no reaction with the matrix or the titanium. The material shows high hardness, high stiffness, and low ductility through precipitation and particle reinforcement.

The energy absorption characteristics of hexagonally packaged circular-celled honeycombs and quadrilater-ally packaged circular-celled honeycombs are obtained under in-plane quasi-static compressive loadings through finite element analysis. The stress–strain curves, deformation modes, energy absorption efficiency, specific plateau stress, normalized energy absorption and energy absorption diagrams are discussed. The cell arrangement patterns influence the shapes of stress–strain curves and deformation modes. The densification strain is in linear relationship with the relative density and the specific plateau stress is proportional to relative density. The hexagonally packaged circular-celled honeycombs have the largest specific plateau stress in the x 2 direction for a given relative density. The normalized energy absorption is nearly proportional to the strain before densification and increases with increasing relative density for a given strain in one compression direction. The envelope line in the energy absorption diagram is approximately a straight line tangent to the shoulder points through the origin. The hexagonally packaged circular-celled honeycombs outperform the quadrilaterally packaged circular-celled honeycombs in in-plane energy absorption.

The effect of hydrogen, and vapors of water and the simplest organic compounds of various classes on the structure of strontium orthocuprate (Sr 2 CuO 3 ) in the temperature range of 150–300 °C has been investigated. At temperatures up to 200 °C, hydrogen and water are embedded in the structure of Sr 2 CuO 3 from the annealing atmosphere. Under these conditions, organic compounds are oxidized to form water followed by hydration of Sr 2 CuO 3 . It has been revealed that Sr 2 CuO 3 is a catalyst for oxidation reactions. Water absorption > 2 wt.% provokes hydrolytic decomposition of Sr 2 CuO 3 with the formation of strontium hydroxide and copper-richer cuprates (SrCuO 2 and SrCu 2 O 3 ). At a temperature of 300 °C, organic compounds partially reduce copper, which is also the cause of the decomposition of Sr 2 CuO 3 .

Damaged or degenerative joints are treated with total joint replacement, however, despite many successful outcomes, significant problems such as implant loosening, and failure occur. These problems occur due to the inability of the implant to support bone cell attachment, delaying the cell–implant interaction affecting bone regeneration. Hence it is recommended to develop and modify implants to induce bone cell proliferation. Herein, we report a self-aligned titania nanotubes–reduced graphene oxide (TiNT–reduced GO) hybrid surface for growth and proliferation of human bone marrow mesenchymal stem cells. The hybrid surface is characterised using electron microscopy, X-ray diffraction and Raman spectroscopy. The human bone marrow mesenchymal stem cell proliferation was studied using standard MTT and fluorescence assays. TiNT–reduced GO hybrid surface, with TiO 2 nanotube of diameter 80 –110 nm and length ⁓500 μm with uniform deposition of reduced GO all over the surface, demonstrated about 50% increased cell growth compared to TiO 2 nanotubes surface. The osteoinductive behaviour of TiNT–reduced GO is observed as these hybrid films support the proliferation of human bone marrow mesenchymal stem cells, hence promising to be a potential implant material for bone regeneration.

The effects of ethylene-vinyl acetate copolymer (EVA) and dicumyl peroxide (DCP) addition on injection moldability and tensile properties of recycled polyethylene (PE) from disposable drip tapes were studied. DCP showed an adverse impact on the injection moldability of recycled PE materials, while EVA had positive effects on it. Tensile properties of the reproduced PE increased with the increasing amount of EVA up to 10 wt.% and decreased beyond it. The DCP addition reduced the elastic properties of the reproduced PE, while it enhanced the tensile strength. Overall, the co-addition of 6 wt.% EVA + 0.4 wt.% DCP could improve the tensile strength of the reproduced PE materials.