Advanced Materials Research Vols. 264-265

Abstract: In this study, the effect of small additions of lithium on the microstructure and morphology of Fe-containing intermetallic compounds in A360 alloy has been investigated. Different Fe contents (1, 1.5 and 2%) were added into A360 alloy, and Li concentrations also varied from 0 to 0.5 wt. %. The image analysis results showed that, the maximum length of β-Al5FeSi plate in Li-modified specimens is changed significantly in comparison with non-modified ones. It is evident that the maximum reduction in the average length of Fe containing platelets occurs in specimens with 2% Fe. Also, the lowest changes in the length of intermetallic phases -as Fe content decreases- occur in the 0.5 wt% Li. At higher Li concentrations, the presence of Al-Li-Si intermetallics in the microstructure can provide undesirable condition. This intermetallic can be so damaging in mechanical properties especially in coarse shapes.

Abstract: This paper reports on an investigation of the relationship between the polishing force and the contact characteristics as the polishing tool approaches the boundary of a part surface during polishing. It was previous established that, for fixed abrasives, when the polishing tool is on the inner surface, the relationship between the polishing force and the pressure at the contact is approximately Hertzian and the contact is a full ellipse. The contact cannot be a full ellipse as the tool touches the boundary. The same polishing force could yield rather different pressure distribution, and thus rate of material removal, within the contact region. A model is proposed to relate the force and the pressure distribution as the tool is close to the edge of a part surface. The model takes into account changes of the contact near the edge. Experimental results are also presented to validate the proposed method.

Abstract: The multi-item single level capacitated dynamic lot-sizing problem consists of scheduling N items over a horizon of T periods. The objective is to minimize the sum of setup and inventory holding costs over the horizon subject to a constraint on total capacity in each period. No backlogging is allowed. Only one machine is available with a fixed capacity in each period. In case of a single item production, an optimal solution algorithm exists. But for multi-item problems, optimal solution algorithms are not available. It has been proved that even the two-item problem with constant capacity is NP-hard, that is, it is in a class of problems that are extremely difficult to solve in a reasonable amount of time. This has called for searching good heuristic solutions. For a multi-item problem, it would be more realistic to consider the setup time, since switching the machine from one item to another would require a setup time. This setup time would be independent of item sequences and this could be a very important parameter from practical point of view. The current research work has been directed toward the development of a model for multiitem problem considering this parameter. Based on the model a program has been executed and feasible solutions with some real life data have been obtained.

Abstract: Computerized machinability data systems are essential for the selection of optimum conditions during process planning, and they form an important component in the implementation of computer integrated manufacturing (CIM) systems. Since statistical models for adhesively bonded tools are unavailable, the present paper presents a study of the development of a tool life, surface roughness and cutting force models for turning constructional steels, using adhesively bonded tools. These models are developed in terms of cutting speed, federate and depth of cut. These variables are investigated using design of experiments and utilization of response surface methodology (RMS).

Abstract: From a series of experiments carried out in this study, the machining characteristic of aeronautical material, titanium alloy Ti6Al4V, under dry orthogonal cutting is determined by the relations among material removal rate (MRR), tool rake angle (), and the other nine parameters in orthogonal cutting concept. Continuous and serrated chip forms are observed and chip form is determined by the flow localization parameter (). It is found that the critical values of  in which serrated chip formed are ranging from  = 4.71 to  = 5.37 or at the chip load from 0.0045 to 0.006 mm2/min. The number of tooth (frequency) on serrated chip increases with cutting speed (V). The tool failure modes found in this study are normal flank wear, notch wear, chipping and catastrophic failure. Tool chip adhesion caused by adhesive wear mechanism and high rake angle weakened the tool cutting edge play important roles on the failure mode of the straight tungsten carbide cutting tool used in this study.

Abstract: The mechanical performance of DLC coatings on 316L stainless steel deposited by a saddle field fast atom beam source has been evaluated using the four point bend (FPB) test. Two different deposition parameters, pressure and current were varied when depositing the films. Load-displacement measurements were carried out during the bend test to determine the load corresponding to crack initiation. This load designated as the cohesive strength of the coating which is also called the cracking resistance of coating and provides a measure of the strength of the coating. The cohesive strength of the coating was calculated based on elementary beam theory. Scanning Electron Microscopy (SEM) was used to determine the location of the crack. Finite element analysis was used to predict the stress distribution across the coating thickness. The experimental work on FPB tests has been used to support the numerical (finite element) model for the determination and prediction of film cohesive strength. It was observed that at lower deposition current, the cohesive strength increases with increased deposition pressure whereas, for higher deposition current, these values do not increase with increasing deposition pressure. The model takes into account the film’s Young’s modulus, thickness and deposition pressure and current, and has shown that it is capable of predicting film cohesive strength when combined with a theoretical formulation for brittle fracture. It has been observed that the maximum stress develops at the outer surface of the film and propagates through the film-substrate interface. This result has only been validated for films with higher Young’s modulus compared to that of the substrate material.

Abstract: The effects of adding a small amount of nano silica in hydroxyapatite (HA) on the sinterability and mechanical properties of hydroxyapatite were studied. The starting HA powder was synthesized using a novel wet chemical precipitation method. Different amount of silica powder was mechanically mixed with the synthesized HA. The green samples were subsequently cold isostatically pressed at 200 MPa. Sintering in air was accomplished by firing the green samples at temperatures ranging from 1050°C to 1250°C. Sintered samples were analyzed to determine phase composition and mechanical properties. The XRD analysis revealed that with increasing the amount of silica in the HA powder, decomposition of HA to TCP occurred at sintering temperature higher than 1050°C. The bulk density of all silica-doped samples decreased through the temperature range studied. In agreement with the bulk density trend, the increasing silica additives in HA depleted the Young’s modulus and Vickers hardness of the HA body. The study revealed that the addition of silica have an adverse effect on the sintered properties of hydroxyapatite bioceramics.

Abstract: The aim of this work is to study the phase stability and sinterability of bismuth oxide (Bi2O3) doped HA ranging from 0.05 wt% to 1 wt%. The green samples were sintered in air at temperature ranging from 1000oC to 1400oC. In this experiment, the results from XRD analysis revealed that the stability of HA phase was disrupted when addition of 0.3, 0.5 and 1.0 wt% Bi2O3 were used and when samples sintered above 1100oC, 1000oC and 950oC, respectively. In general, HA containing 0.5 wt% of Bi2O3 and when sintered at 1000oC was found to be beneficial in enhancing densification, Young’s modulus, Vickers hardness and fracture toughness. Throughout the sintering regime, the highest value of relative bulk density of 98.7% was obtained for 0.5 wt% Bi2O3-doped HA when sintered at 1000oC. A maximum Young’s modulus of 119.2 GPa was observed for 0.1 wt% Bi2O3-doped HA when sintered at 1150oC. Additionally, 0.5 wt% Bi2O3-doped HA was able to achieve highest hardness of 6.04 GPa and fracture toughness of 1.21 MPam1/2 at sintering temperature of 1000oC. Furthermore, the Young’s modulus of HA was found to vary linearly with bulk density.

Abstract: The sinterability of magnesium oxide (MgO) doped hydroxyapatite (HA) ranging from 1 to 10 wt% when sintered at 1150°C was investigated in terms of phase stability, bulk density, Young’s modulus, Vickers hardness and fracture toughness. The addition of up to 1 wt% MgO as sintering additive was found to be beneficial in promoting the densification of HA. Further addition of MgO in the HA matrix would deteriorate its densification properties. Similar results were observed for its stiffness and Vickers hardness. Nevertheless, the fracture toughness of HA was greatly enhanced by the incorporation of 5 wt% MgO. An increased toughness of up to 35% was obtained for the MgO-doped HA when compared to the undoped HA. This improvement is associated to the smaller grain size of the doped sample as compared to the undoped HA.

Abstract: In the present work, densification of synthesised hydroxyapatite (HA) bioceramic prepared via chemical precipitation method was investigated. HA samples was prepared by compaction at 200 MPa and sintered at temperatures ranging from 800°C to 1400°C. The results revealed that the HA phase was stable for up to sintering temperature of 1250°C. However, decomposition of HA was observed in samples sintered at 1300°C with the formation of tetra-calcium phosphate (TTCP) and CaO. Samples sintered above 1400°C were found to melt into glassy phases. The bulk density increases with increasing temperature and attained a maximum value of 3.14 gcm-3 at 1150°C whereas maximum hardness value of 6.64 GPa was measured in HA sintered at 1050°C. These results are discussed in terms of the role of grain size.