Shimaa El-Hadad

Fabrication of Al-Al3Ti/Ti3Al Functionally Graded Materials under a Centrifugal Force

Fabrication of Al-Al3Ti functionally graded materials (FGMs) under the centrifugal force has recently attracted some attention. The controlled compositional gradient of the fabricated FGMs, the low cost of the process, and the good mold filling, are the main advantages of the centrifugal method (CM). Using the conventional CM techniques such as the centrifugal solid-particle method and centrifugal in-situ method, FGMs rings with gradually distributed properties could be achieved. As a more practical choice, the centrifugal mixed-powder method (CMPM) was recently proposed to obtain FGMs containing nano-particles selectively dispersed in the outer surface of the fabricated parts. However, if a control of the particles morphology, compound formulas or sizes, is desired, another CM technique is favored. As a development of CMPM, our novel reaction centrifugal mixed-powder method (RCMPM) has been presented. Using RCMPM, Al‑Al3Ti/Ti3Al FGMs with good surface properties and temperature controlled compositional gradient could be achieved. In this short review, this novel method will be discussed in detail and the effect of RCMPM processing temperature on the reinforcement particles morphology, size and distribution through the fabricated samples, will be reviewed.

Effects of Processing Routes on Wear Property of Al-Al3Ti Alloys Severely Deformed by ECAP

Al-Ti alloys, which have Al3Ti platelet particles in Al matrix, were deformed by ECAP with routes A and Bc. With increasing the number of ECAP passes, Al3Ti platelet particles are fragmented and their sizes decrease. The microstructure of ECAPed Al-Ti alloy specimens by route A has a strong alignment of the fragmented Al3Ti particles. On the other hand, ECAPed Al-Ti alloy specimens by route Bc have a relatively homogeneous distribution of Al3Ti particles comparing with the specimen deformed by route A. Based on these results, it was found that ECAPed Al-Ti alloy specimen by route A has highly anisotropic microstructure. However, both ECAPed specimens with routes A and Bc have no anisotropic wear property. That is because the wear property of the Al-Ti alloy specimen depends on the shape of the Al3Ti particle. From these results, it was found that SPD induced by ECAP is an effective processing method to make homogeneous wear property for the metallic material containing platelet solid-particles.

Surface modification of investment cast-316L implants: Microstructure effects

Artificial femur stem of 316L stainless steel was fabricated by investment casting using vacuum induction melting. Different surface treatments: mechanical polishing, thermal oxidation and immersion in alkaline solution were applied. Thicker hydroxyapatite (HAP) layer was formed in the furnace-oxidized samples as compared to the mechanically polished ones. The alkaline treatment enhanced the precipitation of HAP on the samples. It was also observed that the HAP precipitation responded differently to the different phases of the microstructure. The austenite phase was observed to have more homogeneous and smoother layer of HAP. In addition, the growth of HAP was sometimes favored on the austenite phase rather than on ferrite phase.

Investigation of Wear Anisotropy in a Severely Deformed Al-Al 3 Ti Composite

In the current investigation, Al-Al3Ti composite was processed by equal channel angular pressing (ECAP). ECAP was carried out using routes A and BC up to eight passes of deformation. It was observed that increasing the number of ECAP passes causes fragmentation of Al3Ti platelet particles and decreases their sizes compared to their original sizes in the undeformed Al-Al3Ti specimens. Moreover, the microstructure of route A-ECAPed Al-Al3Ti composite samples showed a strong alignment of the fragmented Al3Ti particles parallel to the pressing axis. On the other hand, ECAPed Al-Al3Ti alloy specimens by route BC have a relatively homogeneous distribution of Al3Ti particles. Because of the platelet Al3Ti particle fragmentation by ECAP, all the ECAPed specimens showed small anisotropy in their wear property in spite of this observed anisotropic microstructure induced by route A-ECAP.

Fabrication of Al/Al3Ti Functionally Graded Materials by Reaction Centrifugal Mixed-Powder Method

Formation of compositional gradient in Al/Al3Ti Functionally graded materials (FGMs) fabricated by the centrifugal method (CM) depends mainly on the centrifugal force and the processing temperature. In this study, a novel centrifugal method, reaction centrifugal mixed-powder method (RCMPM), was proposed to fabricate Al/Al3Ti FGMs under fixed centrifugal force (G=80). The effects of RCMPM processing temperature on the formation of Al3Ti intermetallics, its morphology and its distribution in the fabricated Al/Al3Ti FGMs have been investigated. Fine granular Al3Ti were observed at relatively lower processing temperature while the known coarse platelet-like particles of Al3Ti could be achieved at higher casting temperatures. Moreover, Ti3Al intermetallics compound and unreacted Ti phases are also observed along with Al3Ti particles. In addition, distribution of Al3Ti intermetallics size and their volume fraction showed a significant change when the Al/Al3Ti FGMs processed at different temperatures relative to the liquidus temperature of the master alloy.

Microstructure characteristics and tensile property of ultrasonic treated-thixocast A356 alloy

Billets of A356 aluminum alloy were treated using ultrasonic vibrations during solidification. The billets were reheated to the semisolid state at different routes to optimize the procedure. Billets were, then, thixocast using a die casting machine. The results showed that the ultrasonic-treated billets exhibited finely distributed α(Al) globules after reheating and thixocasting. The thixocast ultrasonic-treated billets showed higher ultimate tensile strength and elongation compared with the untreated billets. Moreover, the thixocast parts showed a tendency to ductile fracture under tension when made from ultrasonic-treated billets, while those made of untreated billets showed brittle fracture with obvious straight facets. These results revealed the feasibility and competence of ultrasonic melt treatment as a potential route for preparing billets for thixocasting.

Effect of Processing Parameters on the Mechanical Properties of Heavy Section Ductile Iron

The main objective of the current work is to investigate the influence of different inoculation conditions on the microstructure and mechanical properties of heavy section ductile iron (DI) castings. Inoculation treatment was done via one step and double step treatments with different amounts of inoculants. The mechanical properties of the fabricated samples were evaluated. The best inoculation procedure in terms of graphite nodules characteristics and mechanical properties was double inoculation with 0.8% inoculants added at first and 0.2% in the late inoculation step. The presence of Sb in one of the cast alloys controlled the growth of graphite nodules in these heavy section ductile iron castings; however low impact toughness was recorded. The matrix structure of ductile cast iron showed a significant influence not only on the strength and impact properties but also on the fracture mode during testing.

Enhancement of wear resistance and impact toughness of as cast hypoeutectic high chromium cast iron using niobium

Abstract The effect of niobium additions on the as-cast microstructure of a hypoeutectic high-Cr cast iron containing 2.2 wt.% C and 16.5 wt.% Cr was investigated. With increasing niobium content, the eutectic M7C3 carbides were refined and became less elongated as well as its volume fraction was decreased gradually. The first precipitated NbC particles could be act as heterogeneous substrate of proeutectic austenite and a barrier to M7C3 grain growth. The morphology of NbC carbides changed with increasing niobium content. Such NbC particles were increased with increasing Nb content and subsequently contributed to increased hardness. Optimum toughness was obtained for the irons alloyed with 2.14% Nb. The effects of applied load and Nb-additions on wear resistance of high chromium cast iron have been studied. The results showed that wear resistance increases with increasing Nb addition. Furthermore, the effectiveness of the NbC particles on the weight loss was more evident at higher loads.

Assessment of Tribological Properties of Cast and Forged Ti-6Al-7Nb and Ti-6Al-4V Alloys for Dental Applications

Thermal oxidation treatment is an easy and environment friendly technique that can be used to harden the surface of titanium alloys, and hence improve the poor tribological properties of these materials. The aim of the present research was to evaluate the tribological behavior of cast and forged Ti6Al7Nb and Ti6Al4V implants after different thermal oxidation treatments. A significant increase in surface hardness of the two alloys was achieved due to the formation of a hard oxide layer and oxygen diffusion zone beneath it. The oxygen diffusion zone, which was generated at 900 °C, showed the best wear resistance in case of Ti6Al4V alloy. On the other side, no remarkable enhancement was observed in the Ti6Al7Nb alloy even at 1100 °C, regardless of the improved surface hardness. In addition, the development of alpha case in the cast samples was different from the forged ones. The widmanstatten microstructure of the cast samples showed thinner alpha case compared to the equiaxed structure of the forged samples in both alloys.

In-vitro and in-vivo, cytotoxicity evaluation of cast functionally graded biomaterials for dental implantology

An innovative technique of casting the titanium implant alloys and its calcium phosphate coating using centrifugal casting method was proposed in the current study. This one-step, self-coating technique results in formation of functionally graded biomaterials (FGBMs) of calcium phosphate/Titanium alloys. Two groups of samples (Group 1 and Group 2) were prepared utilizing self-coated titanium‑niobium (Ti-6Al-7Nb) and titanium- vanadium (Ti-6Al-4V) alloys respectively. The cast samples were then prepared for in-vitro cytocompatibility evaluation, in-vivo systemic toxicity and osseointegration evaluation. Cytocompatibility was examined in-vitro on human bone osteosarcoma cells (Saos-2). In-vivo surgical implantation of the samples in the mandible of the experimental dogs was correspondingly implemented. Tests for systemic toxicity, X-ray images, Dual Energy X-ray Absorptiometry (DEXA) and histopathological analysis were obtained for each dogs mandible sample. In-vitro cytocompatibility studies revealed high cytocompatibility of Group 2 in comparison to Group 1. In-vivo results proved safety of Group 2 as regards to systemic toxicity. On the other hand, results of the X-ray images, DEXA and histopathological analysis revealed comparable osseointegration potential of both groups. These results suggest the use of Group2-FGBMs in dental implant manufacturing and prove that FGBMs prepared by centrifugal casting as self-coated implants have good biocompatibility and osseointegration capability.