Numerical modelling of grain refinement around highly reactive interfaces in processing of nanocrystallised multilayered metallic materials by duplex technique

Microstructure evolution around highly reactive interfaces in processing of nanocrystallised multilayered metallic materials have been investigated and discussed in the present work. Conditions leading to grain refinement during co-rolling stage of the duplex processing technique are analysed using the multi-level finite element based numerical model combined with three-dimensional frontal cellular automata. The model was capable to simulate development of grain boundaries and changes of the boundary disorientation angle within the metal structure taking into account crystal plasticity formulation. Appearance of a large number of structural elements, identified as dislocation cells, sub-grains and new grains, has been identified within the metal structure as a result of metal flow disturbance and consequently inhomogeneous deformation around oxide islets at the interfaces during the co-rolling stage. These areas corresponded to the locations of shear bands observed experimentally using SEM-EBSD analysis. The obtained results illustrate a significant potential of the proposed modelling approach for quantitative analysis and optimisation of the highly refined non-homogeneous microstructures formed around the oxidised interfaces during processing of such laminated materials

Effect of Milling Ball Diameter during Surface Mechanical Attrition Treatment on Microhardness of AISI 316L

Surface mechanical attrition treatment (SMAT) is one of the recently developed techniques to obtain refined grains on metal surface. In this paper, the effect of milling ball diameter during the SMAT on microhardness of AISI 316L is discussed. All samples were treated for 15 minutes. The result shows enhanced microhardness and thickness of hardened layer at the sample's subsurface as the use of larger diameter milling balls</p

Synthesis and evaluation of porous titanium scaffolds prepared with the space holder method for bone tissue engineering

Loss of function and impaired life quality as a result of large bone defects remain a serious problem in the society. Basically, the bone tissue has the capability of healing by itself when fractured. However, impaired healing may occur, leading to delayed union or even non-union when a bone segment is excised above a critical size. In recent years, bone tissue engineering has received increasing attention in the biomedical research community as an alternative approach to bone defect reconstruction. With this approach, damaged bone tissue can be repaired and remodelled with new bone cells at the defect site. For this purpose, a synthetic porous material, namely scaffold, is needed to act as a template to facilitate cellular activities, such as the migrationand proliferation of osteoblasts and mesenchymal cells, as well as the transport of nutrients and oxygen required for vascularization during bone tissue development at the defect site. Currently, titanium is considered to be a preferred biomaterial for bone tissue engineering scaffolds owing to its excellent biocompatibility and mechanical properties. So far, the space holder method has been preferably used for the fabrication of titanium scaffolds with high porosity and open, interconnected pores for bone tissue engineering. Despite a large number of studies on the scaffold fabrication with this method, the mechanisms involved and the way to control the porous structure of scaffolds during fabrication have not yet been fully understood.Biomaterials & Tissue Biomechanic

Fabrication of metallic biomedical scaffolds with the space holder method: A review

Bone tissue engineering has been increasingly studied as an alternative approach to bone defect reconstruction. In this approach, new bone cells are stimulated to grow and heal the defect with the aid of a scaffold that serves as a medium for bone cell formation and growth. Scaffolds made of metallic materials have preferably been chosen for bone tissue engineering applications where load-bearing capacities are required, considering the superior mechanical properties possessed by this type of materials to those of polymeric and ceramic materials. The space holder method has been recognized as one of the viable methods for the fabrication of metallic biomedical scaffolds. In this method, temporary powder particles, namely space holder, are devised as a pore former for scaffolds. In general, the whole scaffold fabrication process with the space holder method can be divided into four main steps: (i) mixing of metal matrix powder and space-holding particles; (ii) compaction of granular materials; (iii) removal of space-holding particles; (iv) sintering of porous scaffold preform. In this review, detailed procedures in each of these steps are presented. Technical challenges encountered during scaffold fabrication with this specific method are addressed. In conclusion, strategies are yet to be developed to address problematic issues raised, such as powder segregation, pore inhomogeneity, distortion of pore sizes and shape, uncontrolled shrinkage and contamination.Biomechanical EngineeringMechanical, Maritime and Materials Engineerin

Effect of surface mechanical attrition treatment (SMAT) on microhardness, surface roughness and wettability of AISI 316L

Surface roughness and wettability are among the surface properties which determine the service lifetime of materials. Mechanical treatments subjected to the surface layer of materials are often performed to obtain the desired surface properties and to enhance the mechanical strength of materials. In this paper, the surface microhardness, roughness and wettability of AISI 316L stainless steel resulting from surface mechanical attrition treatment (SMAT) are discussed. The SMAT was conducted with various processing parameters, including the duration of treatment, the number and diameter of milling ball, and the motor speed of the SMAT machine. The result indicates an increasing surface microhardness due to the SMAT. A harder surface is yielded by the SMAT with a longer duration, a bigger and a larger number of milling balls, and a higher vibration frequency. The SMAT also creates craters on the steel surfaces which correspond to the increasing roughness from 0.046 mu m to the values in ranging from 0.681 to 0.909 mu m. The change on the surface roughness by the SMAT does not only depend on the duration of treatment, but also the other processing parameters. In addition, the wettability of AISI 316L surface slightly increases by the SMAT as seen on the decreasing droplet contact angle from 88.6 degrees to the values ranging from 74.4 degrees to 87.0 degrees. Such a droplet contact angle reduction is related to the increasing surface roughness after the SMAT. In conclusion, this study reveals the possibility of the SMAT to be used for surface properties optimization in addition to the strength enhancement of stainless steel. (C) 2010 Elsevier B.V. All rights reserved

Effect of chemical composition on hot cracking susceptibility (HCS) using various hot cracking criteria

The paper aims to evaluate the effect of chemical composition on the Hot Cracking Susceptibility (HCS) using mechanical and non-mechanical hot cracking criteria during solidification. The criteria were SKK as a mechanical criterion. Feurer, Clyne Davis, and Katgerman as non-mechanical criteria. The criteria were implemented at various parameters to evaluate their abilities in the hot cracking susceptibility (HCS) prediction at varied chemical composition. In this study, The Mg content was varied in Al9Zn (1, 1.5, 2, 2.5 %wt.) Mg2Cu alloys and Cu content in Al9Zn2Mg (1, 1.5, 2, 2.5 %wt.) Cu alloys. The validation of the result is also conducted by comparing with the experimental data. Based on Feurer criterion, The hot cracking initiates at lower temperature and at higher critical rate of feeding and shrinkage with Cu content, and the hot cracking initiates at higher temperature with Mg content, and it initiates at higher critical rate of feeding and shrinkage from 1 up to 1.5 of Mg, and the critical rate of feeding and shrinkage remains constant from 1.5 up to 2.5 of Mg. Based on Clyne &amp; Davies, the HCS decreases with Cu content from 1 up to 2 of Cu, and it increases from 2 up to 2.5 of Cu. The HCS decreases with Mg content from 1 up to 2 of Mg, and it remains constant from 2 up to 2.5 of Mg. Based on Katgerman criterion, the HCS decreases with Cu content from 1 up to 1.5 of Cu, it increases from 1.5 up to 2 of Cu, and it decreases from 2 up to 2.5 of Cu. The HCS decreases sequentially with Mg content. Based on SKK criterion, the HCS curves shift to the right with Cu content which means that the hot cracking initiates at lower temperature, and the HCS curves shift to the left with Mg content which means that the hot cracking initiates at higher temperature with Mg content. The Feurer, Clyne &amp; Davies, and some specific range for SKK criteria are in agreement for the effect of Cu content on HCS of alloys, and Katgerman and some specific range for Clyne&amp;Davies criteria are in agreement for the effect of Mg content on HCS of alloys.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Team Joris Di