B. Arifvianto

Effect of cold working and sandblasting on the microhardness, tensile strength and corrosion resistance of AISI 316L stainless steel

The aim of this work is to investigate the effect of cold working and sandblasting on the microhardness, tensile strength and corrosion rate of AISI 316L stainless steel. The specimens were deformed from 17% to 47% and sandblasted for 20 min using SiC particles with a diameter of 500–700 μm and an air flow with 0.6–0.7 MPa pressure. The microhardness distribution and tensile test were conducted and a measurement on the corrosion current density was done to determine the corrosion rate of the specimens. The result shows that the cold working enhances the bulk microhardness, tensile and yield strength of the specimen by the degree of deformation applied in the treatment. The sandblasting treatment increases the microhardness only at the surface of the specimen without or with a low degree of deformation. In addition, the sandblasting enhances the surface roughness. The corrosion resistance is improved by cold working, especially for the highly deformed specimen. However the follow-up sandblasting treatment reduces the corrosion resistance. In conclusion, the cold working is prominent to be used for improving the mechanical properties and corrosion resistance of AISI 316L stainless steel. Meanwhile, the sandblasting subjected to the cold worked steel is only useful for surface texturing instead of improving the mechanical properties and corrosion resistance.

Characterisation of space holder removal through water leaching for preparation of biomedical titanium scaffolds

Abstract Scaffolds for bone tissue engineering are highly porous materials having interconnected and homogeneously distributed pores to facilitate the formation of new bone tissue. At the same time, appropriate mechanical strength is required in the scaffolds to withstand stresses in the in vivo environment. The space holder method has been used to fulfil these contradictory requirements in the fabrication of titanium scaffolds. Space holding particles are mixed with titanium particles then removed before or during sintering, to leave pores in the scaffolds. Despite its importance, the removal of space holders has rarely been studied. In the present study, removal by water leaching was investigated. Leaching was characterised using a novel real-time measurement technique adopted from ASTM B963-08 that achieved precise scaffold weight loss data reflecting the removal of space holding particles. The acquired data fit existing solvent debinding models for powder injection moulded parts, allowing the mechanism involved during water leaching to be determined.

Effect of Sandblasting and Surface Mechanical Attrition Treatment on Surface Roughness, Wettability, and Microhardness Distribution of AISI 316L

Surface roughness and wettability determines the stability of bone-implant integration. Stable implants can be found in those with a rough and hydrophilic surface. Sandblasting and surface mechanical attrition treatment (SMAT) are among the current techniques to obtain surface with such typical properties. In addition, both treatments increase mechanical strength of metal through surface grains refinement. In this paper, the effect of sandblasting and SMAT on surface roughness, wettability, and microhardness distribution of AISI 316L is discussed. All treatments were conducted for 0-20 minutes. The result shows a rougher and a more hydrophilic surface on the sandblasted samples rather than on those with SMAT. A harder surface is yielded by both treatments, but the SMAT produces a thicker hardened layer.

Surface modification of titanium using steel slag ball and shot blasting treatment for biomedical implant applications

Surface modification is often performed using grit or shot blasting treatment for improving the performances of biomedical implants. The effects of blasting treatments using steel slag balls and spherical shots on the surface and subsurface of titanium were studied in this paper. The treatments were conducted for 60–300 s using 2–5 mm steel slag balls and 3.18 mm spherical shots. The surface morphology, roughness, and elemental composition of titanium specimens were examined prior to and after the treatments. Irregular and rough titanium surfaces were formed after the treatment with the steel slag balls instead of the spherical shots. The former treatment also introduced some bioactive elements on the titanium surface, but the latter one yielded a harder surface layer. In conclusion, both steel slag ball and shot blasting treatment have their own specialization in modifying the surface of metallic biomaterials. Steel slag ball blasting is potential for improving the osseointegration quality of implants; but the shot blasting is more appropriate for improving the mechanical properties of temporary and load bearing implants, such as osteosynthesis plates.

Material Removal and Fracture Detection in Micro-EDM Processes

The important thing in micro-machining is its accuracy. The Micro-Electrical Discharge Machining (micro-EDM) is a promising method in micro-machining, because (1) the process is independent on the hardness of the workpiece but only depends on its thermal conductivity and melting point and (2) it can be used to machine materials with highly complex geometrical shapes using a simple-shaped tool electrode. However, the process in micro-EDM is not totally well-known, especially related to the formation of discharge pulse energy and the fracture phenomena. In the micro-EDM processes, the formation of discharge pulse energy is a complex phenomenon, since it is related to many parameters such as discharge gap, charge voltage, capacitance, and tool electrode wear. In this paper, the Acoustic Emission (AE) sensor is used to detect the changes of discharge pulse energy during machining of brass using micro-EDM. The results shows that the AE signals can detect and explain the fracture phenomena during the micro-EDM processes.

Contouring posterior and lateral tibia of javanese people based on X-Rays images

Osteosynthesis plates provide a rigid and stable fixation for bone fracture treatment. The bone stability during the fixation period is determined by the conformity between the bone and plate. The plate fits well to the bone if it is designed based on the bone contour. Hence, the contour profile of bone must be determined prior to designing the plate. The aim of this work is to perform a contouring technique for human tibia and then to formulate the results into a mathematical model. Samples were 2D X-rays images of five tibia from Javanese people. The data was well fitted to the Rational Chebyshev equation.

Hybrid surface treatment for improving mechanical and surface properties of AISI 316L stainless steel

Failures of osteosynthesis plate are often dealing with overloading and fatigue fracture. Efforts have been made to improve the strength of the plate. In addition, surface roughness is also a matter of concern which relates to biocompatibitlity of the plate. In this study, a hybrid surface treatment consisting of surface mechanical attrition treatment (SMAT) and electropolishing is used to improve the strength and surface properties of AISI 316L stainless steel; a typical biomaterial used for osteosynthesis plate. The SMAT was performed using 250 steel balls with diameter of 4.36 mm for 0 – 20 minutes. The following electropolishing treatment was conducted after the SMAT for 0 – 20 minutes. The subsurface microhardness and surface roughness were measured to evaluate the change in mechanical and surface properties of AISI 316L after the treatment, respectively. The result shows that the SMAT enhanced surface microhardness from Hv = ±1.4 GPa to ±2.9 GPa, but remained to yield a rough surface (Ra = ±1 µm). The roughness and subsurface microhardness decreased from Ra = ±1.0 µm to ±0.1 µm and from Hv = ±2.9 GPa to ±2.2 GPa, respectively. In conclusion, the hybrid surface treatment in this study is able to improve both surface and mechanical properties of AISI 316L stainless steel.