The effect of porosity on the mechanical properties of Ti–8Nb–8Zr–8Cu alloy

Inclusions in metal materials are often problematic. For instance, the presence of hard non-metallic inclusions in aluminum alloys can not only degrade the mechanical properties of the final product but also create a number of other processing-related problems in diecasting such as excessive tool wear [1], increased sensitivity to porosity formation [2], poor surface finish and lack of pressure tightness. A great deal of effort has been expended over the years on the identification, quantification and removal of these inclusions [3–5] and significant progress has been made. Recently, Nissan Casting Australia Pty Ltd (NCAP) sponsored a research project to examine the effects of molten metal quality on the quality of high pressure diecastings. Experimental results showed that the porosity level in the castings increased as the number of inclusions in the melts increased [6]. These inclusions were found to consist predominately of an unknown type of aluminum oxide. This letter documents the results of the characterization of this aluminum oxide. Metal used in the high pressure diecasting industry is primarily recycled aluminum produced from various types of scraps. In the case of the foundry in this study, molten metal prepared by the recycling plant is delivered directly to the high pressure diecasting plant ready to be used for production. The alloy is a Japanese standard: ADC12. In order to efficiently examine inclusions present in the aluminum, it is necessary to concentrate them from a small sample of the molten metal [7]. This is realized by utilizing PoDFA (porous disk filtration apparatus) [8]. About 1 kg of molten aluminum contained in a crucible is forced to flow under pressure through a fine ceramic filter (mounted at the bottom of the crucible). Inclusions present in the molten metal are collected on the surface of the filter forming an inclusion cake (Fig. 1 is an optical micrograph showing a cross-section of a portion of a large inclusion cake). The used filter with inclusions collected on its surface forms a sample which can be analyzed using normal metallographical procedures. Samples were taken from various melts including those as-delivered, remelted, untreated and treated in various vessels such as holding furnace, transfer ladle and degassing station. Most of the inclusions found in aluminum melts have been identified and well documented [3]. BOMEM Inc. (Quebec, Canada) has compiled an inclusion library which is supplied to PoDFA users to assist in the identification of inclusions. Most types of inclusions can be readily identified under the optical microscope either by experience or by comparison with images from the inclusion library based on shape, color and other morphological characteristics. However, if the inclusions cannot be identified by these means, then other techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray analysis and X-ray diffraction (XRD) may be necessary for their identification. After being polished, the PoDFA samples were first examined using optical microscopy. It was found that the majority of inclusions appear as dark particles under the optical microscope (see the band of dark particles in Fig. 1 and similar particles in higher magnification image Fig. 2) along with some typical oxide films and sludge particles. These particles are typically 10–50μm in size with morphology similar to spinel crystal listed in the BOMEM Inc inclusion library. The samples were further examined using SEM (Leica S440). Fig. 3 presents a secondary electron image (a) as well as a backscattered electron image (b) of the inclusions found in a PoDFA sample. The inclusions appear to be black in the backscattered electron (BSE) image indicating that they have a lower mean atomic number than the aluminum matrix (grey). The bright phase in Fig. 3b is an Febearing intermetallic compound [9, 10] (often called “sludge”). It is interesting to note that some of the dark particles are within the sludge particles, suggesting that the dark particles may have acted as nucleation sites for the formation of sludge particles. X-ray analysis using energy dispersive spectroscopy (Oxford Link ISIS equipped in Leica S440 SEM) showed that the dark particles mainly contain: O and Al with a minor amount of P, and in some samples, a minor or trace amount of Ca (see Fig. 4), indicating that they are some type of aluminum oxide. (The X-ray spectrum acquired from the PoDFA filter grains which is corundum showed no P under similar counts). Fig. 5 shows the X-ray spectrum of a sludge particle.

This study aims to produce pure titanium with differing porosity levels for use as a load-bearing implant material that can mimic natural bone structure. Ti + x space holder agent (x: 0, 5, 15, and 20 wt.%) samples were prepared via powder metallurgy route, employing a pressure of 300 MPa followed by sintering at 1200 °C for 6 h. Effect of the space holder agent on the pore characteristics, phase constituent, and mechanical performance, including elastic modulus and ultimate compressive strength, were investigated. Microstructural characterizations were conducted, employing an optical microscope, scanning electron microscopy and energy dispersive spectroscopy. The phase structure was characterized by X-ray diffraction. Additionally, the mechanical behaviour of the samples achieved was assessed by uniaxial compression test at room temperature. The results from the current studies revealed that adding space holder agent effectively modified the porosity level and pore characteristics without altering the phase constituent of the samples. As the space holder agent content was increased from 0 to 20 (wt.%), the porosity level of the samples increased from 18 % to 56 %, while the ultimate compressive strength values reduced significantly from 1,236 MPa to 112 MPa.

On characterizing the mechanical properties of aluminum–alumina composites

High temperature failure of natural gas feed burner pipe

Microstructure, crystal structure and electrical properties of Cu 0.1Ni 0.8Co 0.2Mn 1.9O 4 ceramics obtained at different sintering conditions

Although delta ferrite is a very common phase in most austenitic stainless steels, studies about its formation and evolution during slab processing from industrial heats of tens of tons are scarce. The main objective of this research is to study the evolution of delta ferrite (quantity, chemical composition, morphology, and distribution) along the production route from the cast slab to the coil of an industrial heat of 80 tons of 304 stainless steel. Samples were extracted after the following processing steps: continuous casting, first and second hot-rolling pass, and solution-heat-treating, arriving at the final commercial condition. Sample analyses were carried out with several complementary microstructural characterization techniques: optical microscopy, scanning electron microscopy with energy dispersive spectroscopy (EDS), X-ray diffraction, and magnetic measurements of delta ferrite content (feritscope). Thermocalc® indicates that the present continuous cast slab solidifes according to the FA (ferrite-austenite) mode and the final microstructure should be completely austenitic in equilibrium conditions. Nevertheless, delta ferrite is detected along the processing steps, indicating that the steel is out of phase equilibrium. The ferrite content measured after solidification varies significantly across the as-cast slab thickness. Lower values are detected on the surfaces, followed by a gradual increase when moving into the slab, reaching a peak, and finally decreasing at the slab center. This pattern of delta ferrite content is named “M type” distribution. The average content of delta ferrite decreases after each subsequent processing step, namely the two hot-rolling passes and the solution heat-treating.

In order to improve the hardness and surface properties of TC4 titanium alloy, in-situ synthesis by laser cladding is used in this paper. A TiC-TiBx reinforced intermetallic composite coating was fabricated on Ti-6Al-4V titanium alloy by laser cladding with preplaced the high purity B4C, Ti and Ni powders. The microstructure, morphology and composition of the composite coating were analyzed by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD). The Tafel polarization tests and dry sliding wear tests were employed to study the corrosion and wear behaviors of the composite coating. The results show that the coating has good metallurgical bond with the substrate, both crack and air hole are not found. The composition of the coating includes in-situ synthesis TiC-TiBx and TiNi-Ti2Ni dual phase intermetallic composite. The microhardness increases from 300 HV0.2 for the substrate reaching a peak as high as 930 HV0.2 for hard particles reinforced intermetallic composite coating. The wear resistance of the coating is improved significantly, due to combined action of hard ceramic reinforcements and ductile intermetallic matrix. While the untreated titanium alloy shows a passive behaviour, the composite coating reveals high electrochemical inertia and low corrosion currents. The strengthening mechanism of cladding is also studied.

A 234 steel flange ASTM is widely used in oil and gas. A damage flange from a unit of submersible pump operated at an offshore platform. The leakage was occurred at the flange connection at submerged part of the vertical pump. The external protection of the section was external coating. The leakage had occurred twice at the same vertical pump. The present investigation aims to analyze the main cause of the failure by conducting a standard failure analysis test including chemical composition test, visual examination, microstructural examination by optical microscope and scanning electron microscope (SEM) equipped with energy-dispersive spectroscopy (EDS), X-ray diffraction and Brinell hardness measurement. The results of this investigation on the failed flange showed that the microstructure of the flange material is found to be ferrite-pearlite with banded structure on the pearlite. This banded structure influences the corrosion properties of the material. It is found that pearlite banded structure increase the corrosion rate of carbon steel. However, the damage mechanism could be due to Galvanic Corrosion and Crevice Corrosion. These two mechanism are possible to the flange joint between the bowl and column. The bowl is known as Nickel-Aluminum-Bronze (NAB) while the column is carbon steel (CS).

This research article presents the procedure for the fabrication of Aluminium alloy (LM25) based metal matrix composites containing particulates of silicon carbide (10 wt. %) and nickel (0, 5 and 10 wt. %). Using the vortex casting technique, three composites were formulated and characterized as per ASTM standards. Microstructure analysis using "scanning electron microscopy" reveals the uniform distribution of reinforcing particulates within the base matrix without clustering. "Energy dispersive spectroscopy" illustrates the presence of ingredients within the composites. "X-ray diffraction" patterns indicate the formation of mesoporous NiSiAl compound within the composite resulting from internal reactions. The "optical microscopy" reveals the refinement of grain structure with the inclusion of nickel particulates within the composites. The influence of the composition of reinforcing particulates that is, silicon carbide and nickel on the properties of the base matrix was explored. An enhancement in the microhardness, tensile strength, wear resistance and traction force and a reduction in friction coefficient was observed together with a marginal reduction in elongation and the porosity level is also under the controlled limits (<5%).

Metal matrix composites (MMCs) play a crucial role in the aerospace, automotive and mineral processing industries. The properties of aluminum matrix composites (AMC) that are renowned for their high strength, good stiffness and excellent thermal conductivity can be enhanced by incorporating various reinforcements. In this investigation, Al7075 alloy with TiC (3, 6, and 9 wt.%) reinforcements was processed via stir casting. Optical microscope (OM) and scanning electron microscope (SEM) were utilized to study the microstructural changes. The chemical composition and phases were analyzed using energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) respectively. Evaluations were conducted on properties such as hardness, tensile strength, corrosion and wear behavior. On increasing the wt.% of TiC from 3 to 9 wt.%, it was observed that the hardness increased by 11%, the tensile strength increased by 200%, and the wear rate decreased by 50%. The composite containing 9 wt.% TiC had the lowest corrosion resistance.

Fabrication and properties of extruded and sintered BeO

Experimental partial phase diagram of the Zr–Sn–Fe system

In this present study, wear behaviours of high chromium white iron valve seat inserts and tappets used in the automotive sector were investigated. Wear behaviours of three different rates of high chromium white cast irons (containing 10, 12 and 14% chromium) were examined under heavy service conditions. For that purpose, the produced valve seat inserts were characterized through Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X-ray diffraction (XRD) and hardness measurements. They were tested at a sliding speed of 1 ms−1, under 120 N load and for six different sliding distances (500, 1000, 1500, 2000, 2500, 3000 m) by using a standard wear apparatus (pin-on-disk type). The result showed that as the amount of Cr increased in the alloys, their hardness decreased. The decrease in the hardness were considered to be as the result of transformation of M7C3 carbides into M23C6 carbides in the structure. This decrease in hardness with increasing chromium content also increased the weight loss. Thus, it was determined that the white iron with 14% Cr (which had a greater amount of M23C6 carbides) was subjected to the highest wear.

Ti6Al4V has been widely used as the orthopedic implant material due to its excellent mechanical properties and biocompatibility. However, failure in the long-term use of Ti6Al4V implants may occur as a result of the “stress shielding effect” which caused by the difference elastic modulus between the implant and the bone. Therefore, porous Ti6Al4V is developed to achieve lower elastic modulus but maintain other interesting properties. To produce porous Ti6Al4V, powder metallurgy (PM) using the space holder can be chosen as a pore former. The problem of Ti6Al4V fabrication may arise due to the high reactivity of titanium at a high temperature. Therefore, PM using arc plasma sintering (APS) method is proposed to reduce the risk of oxidation and contamination in porous Ti6Al4V manufacturing in a relatively shorter time. In this study, carbamide was varied (0-20 wt.%) to prepare porous Ti6Al4V while the APS processing parameters were kept at a constant value (current of 40 A, sintering time of 8 minutes). The as-sintered specimens were then characterized by scanning electron microscopy (SEM)-energy dispersive X-ray spectroscopy (EDS) analysis and X-ray diffraction (XRD). It was shown that the carbamide can be used to fabricate porous Ti6Al4V via the APS method. Addition of carbamide was in line with the increasing of porous formation in the alloy. From this study, Ti-15 Carb was shown to be a potential porous Ti6Al4V alloy due to its highly distributed pore structure while having less contamination and oxidation.

In this study, aluminum doped lead sulfide (PbS:Al) thin films were deposited on soda lime glass substrates using chemical bath deposition (CBD) technique. The structural, morphological, optical and electrical properties of as-deposited PbS thin films were studied as a function of Al concentration (0, 2, 4, 6, 8 at. %). The deposited films can be analyzed using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), x-ray diffraction (XRD), UV-Vis-NIR spectroscopy and Hall measurement. From SEM, it was evident that the thickness of the films decreased from 750 nm (0 at. %) to 280 nm (8 at. %) with increased Al concentration. XRD analysis revealed that the prepared films exhibited face centered cubic structure without any other binary phases. The average crystallite size of the films decreased from 33.71 to 20.45 nm. The direct optical band gap values were increased from 0.90 to 1.29 eV. The optical parameters such as refractive index (n), extinction coefficient (k), real (ɛ 1) and imaginary (ɛ 2) parts of the dielectric constant were 1.51–2.04, 0.0035–0.0075, 2.50–6.20 and 0.005–0.16 respectively. The absorption coefficient (α) of all the deposited films was in the range of ≈105 cm−1. The electrical resistivity of the deposited films was found in the range of 102–103 Ω·cm. The overall analysis indicate that the deposited PbS:Al thin film shows promise as an absorbing layer for heterojunction solar cell devices.