Sintering Characteristics of a Powder Injection Molded Ceria-Stabilized Zirconia–Mullite Composite

Powder injection molding (PIM) technology has the potential for economically manufacturing several complex-shaped zirconia–mullite components in mass production. The sintering behavior of a zirconia–mullite composite fabricated by injection molding was analyzed in this paper. The focus of this study is to assess the dependence on properties and microstructure on PIM processing conditions. The sintered density of the samples displayed a strong dependence on sintering temperature. The hardness of the samples followed a similar trend as sintered density. A maximum fracture toughness of 4.1 ± 0.3 MPa · m^1/2 and strength around 450 ± 60 MPa was observed for samples sintered at 1500°C for 4 h. The properties from this study are significantly higher than the values reported in majority of the prior studies where other technologies like uniaxial and cold isostatic pressing were used to fabricate zirconia–mullite composites. The above results support the suitability of PIM as a manufacturing process for complex-shaped zirconia–mullite components with good mechanical properties.     

Synthesis and Characterization of MgB2 Thin Films Prepared by?2.4?Mhz Ultrasonic Spray Pyrolysis System

Nano-sized B and Mg powders have been successfully deposited onto single crystal MgO(100) and Al₂O₃(001) substrates using 2.4 MHz ultrasonic spray pyrolysis system and an appropriate solution to obtain thin films of MgB₂ superconductors. After an in-situ heating process, ??600?C1000 nm thick superconductor films were obtained. The microstructure, electrical, and magnetic properties were characterized by means of particle size analyzer, XRD, SEM?CEDX, R?CT, and M?CH analysis. The effect of particle concentration in the solution, spraying time, and heating temperature on the quality of the MgB₂ films were discussed. The best T _c and T _zero results were obtained to be 39.5 and 37.4 K, respectively, for the film deposited on the Al₂O₃(001) substrates. Magnetic properties of the MgB₂ films were investigated at 3 different temperatures and up to 5 T. Symmetric hysteresis loops for all temperature and field cases were obtained and maximum $J_{c}^{\mathrm{mag}}$ value was calculated to be 4.0×10⁶ A?cm^?2 at 10 K for 0 T for the film deposited on the Al₂O₃(001) substrates. The results obtained were found to be highly dependant on the particle concentration in the solution, heating temperature of substrates and carrier gas flow rate during spraying.     

Influence of Process Parameters on Cu–Fly Ash Composite by Powder Metallurgy Technique

In this study influence of compaction pressure, sintering temperature, and sintering time on mechanical and wear behavior of the fly ash reinforced copper-based composites are analyzed. The composites were prepared by powder metallurgy (P/M) technique with copper as matrix, 5 and 10 wt% of fly ash as reinforcement. The green compacts were prepared at three different pressures such as 350, 400, and 450 MPa. The prepared green composites were sintered at 700, 800, and 900 °C for the time period of 30, 60, and 90 min, respectively. From the results it is observed that when the process parameter increases the density, hardness, compression strength, and wear resistance increases.     

Investigation of Sintering Technology for Composite of Stainless Steel and Partially Stabilized Zirconia

The sintering technology for mixed powedered extrusion rods of different proportions of stainless steel to magnesia partially stabilized zirconia(PSZ) was investigated..The effects of some sintering parameters including holding time ,atmosphere and protective gas pressure on shrinkage,relative density,micostructure,micro-Vickers hardness and compression strength of sintered samples were mainly researched.The experimental results are as follows(1)The shrinkage and the relative density of the sintered samples decrease as increasing stainless steel content in the composite,except for the xase containing 90 percent of stainless steel;(2)The porosity in PSZ matrix rises as increasing the stainless steel content in the composite;(3)Longer sintering holding time ,higher sintering vacuum and gas-pressure sintering process not only enhance the relative density ,but also improve microstructure of composite;(4)Micre-Vickers hardness of PSZ matrix decreases as increasing stainless steel content,while that of stainless steel particles in sintered samples varies unnoticeably.     

Technique of Aluminum Alloy Composite by Inversion Casting

The influence of the temperature of liquid aluminum alloy,the dipping time in liquid alloy and the thickness of base strips on the solidified layer was studied during the process of producing aluminum alloy composite strips used in automobile radizator with inversion casting.It is concluded that there is welding as well as diffusion of alloying elements between the base strip and the coating.Experiments proved that the interface has a good bonding.     

Superior Properties of Mg–4Y–3RE–Zr Alloy Prepared by Powder Metallurgy

Magnesium alloys are important materials for application in the automotive and aviation industries. During the last few years, the number of possible applications as biodegradable implants in medicine has grown. Mg–RE(rare earth) alloys belong to the most advanced group of products, offering the best combination of mechanical properties and corrosion resistance. Among these materials, WE43(Mg–Y–Nd)is a very well-known commercial alloy that has been extensively studied for applications at increased temperatures and also in organisms. Although this material has been described, there are still possibilities to improve its properties and subsequently expand its applicability. Powder metallurgy has already been used for the preparation of magnesium alloys with superior mechanical properties and occasionally superior corrosion properties. Therefore, the present paper is oriented toward the preparation of Mg–4Y–3RE–Zr(WE43) alloy by the powder metallurgy technique(WE43-PM) and comparison of the final properties with the product of extrusion of as-cast ingot(WE43-IM). Our processing leads to a partial improvement in the mechanical properties and superior corrosion resistance of WE43-PM. The texture strength of WE43-PM was low, and therefore, anisotropy of mechanical properties was suppressed.     

Plasma Spray Forming of Nanostructured Composite Coatings

The nanostructure composite coating is obtained via plasma spraying of Al2O3-13wt pct TiO2 powder.Brittle and hard lamella results from melted nanostructured powder.Ductile nanostructured matrix forms from unmelted nanostructured particles.Through the adjustment of constituent and nanostructure,hardness/strength and tough-ness/ductility are balanced and overall properties of the structure composite are achieved.     

Structural,Electrical and Dielectric Properties of Co–Mn Spinel Nanoferrites Prepared by Co-precipitation Technique

Cobalt manganese nanoceramics with nominal composition Co_1−x Mn _x Fe₂O₄ (x=0.00, 0.15, 0.30, 0.45, 0.60, 0.75) were synthesized by a chemical coprecipitation technique. The X-ray diffraction patterns revealed the cubic spinel structure. The average crystallite size from the Sherrer formula was in the range of 28 nm–56 nm. The lattice parameter increased with a concentration of manganese. Scanning electron microscopy (SEM) was used for microstructural study. The electrical properties such as electrical resistivity (ρ), drift mobility (μ _d), and activation energy (ΔE) were measured using a two-probe apparatus in the temperature range 323–573 K. The electrical resistivity decreased with temperature and manganese concentration. The dielectric constant (ε′), loss factor or imaginary loss (ε″) and dielectric tangent loss (tan δ) were measured at room temperature using a LCR meter in the frequency range 100 Hz to 5 MHz. All the dielectric parameters decreased with increasing frequency. The AC electrical conductivity (σ _ac) was calculated from the dielectric measurements. It increases with increase of frequency and manganese concentration. The increase in electrical conductivity may be attributed to the formation of Co⁺³ and Mn⁺³ from Co⁺² and Mn⁺³, respectively, at both A and B sites.     

Production of Ti–13Nb–13Zr Alloy by Powder Metallurgy (P/M) via Sintering Hydrides

The blended elemental method was selected for the manufacture of Ti–13Nb–13Zr alloy by a cold isostatic pressing process and sintering densification under high vacuum. The samples were sintered at the different temperatures from 1250°C to 1450°C with a pressure of 10^?3 ～ 10^?5 Pa. The decomposition of titanium, niobium, and zirconium hydride powders was discussed by thermal gravimetric analyses and differential scanning calorimetry. The phase composition, microstructure and fracture morphology of Sintered Ti–13Nb–13Zr samples were determined by X-ray diffraction and scanning electron microscopy. The results indicate that the hydrogen can be removed effectively. Chemical analysis shows that the Nb, Zr alloying element and hydrogen contents accord with the standard of the ASTM-1713. The final density of sintered Ti–13Nb–13Zr specimens is 4.99 g cm^?3 after sintering at 1450°C for 4 h, representing 99.69% of the theoretical density. The microstructure of sintered Ti–13Nb–13Zr alloys by powder metallurgy is a typical Widmannstätten (α + β).     

Estimation of Pore Charge on Zirconia Membrane Prepared by Sol-gel Route Using Zeta Potential Measurement

Zirconia membrane was prepared in the sol-gel process by filtering viscous colloidal zirconia sol through microporous alumina support and gelling followed by sintering at 743 K. The scanning electron micrograph show that mean pore size was 543 nm and pore density was 1.47×107/cm2.The filtration characteristics during membrane layer formation showed that the membrane layer formation started after 40 min. The membrane layer thickness and the porosity of the membrane were determined gravimetrically by finding out the amount of water present in the pores. The membrane layer thickness was found to be 3 micron and the porosity was found out to be 0.38. The pore charge density was estimated from the particle charge density, pore density, pore diameter and the thickness of the membrane layer.     

Characterization and Magnetic Properties of Cobalt Nano-Particles Prepared by Metal Vapor Synthesis Technique

The metal vapor synthesis technique was employed to prepare Co nanoparticles. The characteristics and properties of the particles were studied by transmission electron microscopy, X-ray diffraction, temperature-programmed desorption,chemisorption and magnetic measurements. The experimental results showed that the particle size of Co powders depended on the initial Co concentration in the toluene matrix, reaching average crystallite diameter of 1.5 nm for the highest concentration (6.4 at. pct) investigated. The particles with size of 10 nm exist, due to the agglomerates of microcrystallites. The Co particles were surrounded by a thin carbonaceous layer formed due to toluene decomposition on cocondate melt-down and subsequent warming to room temperature. The carbonaceous layer was composed primarily of C1 fragments. The Co powders demonstrated ferromagnetic behavior.     

Microstructure and Mechanical Properties of Tic/NiCrMo Cermets Produced by Liquid Sintering Technique

The effect of M additions on the microstructure and mechanical properties of TiC-based cermet produced by li oquid sintering method of powder metallurgy was investigated. The Mo content was varied between 0 and 0.8 wt.%, in 0.2wt.% increments. These flaws drastically decreased with increasing Mo content. As in conventionally produced materials, Mo was found preferentially on the carbide phase. Mo-rich regions due to incomplete dissolution of large Mo agglomerates were observed.     

Study of Thermal Fatigue Resistance of a Composite Coating Made by a Vacuum Fusion Sintering Method

Thermal fatigue behavior of a Ni-base alloy chromium carbide composite coating made by a vacuum fusion sintering method are dicussed,Results show that thermal fatigue behavior is associated with cyclic upper temperature and coating thickness,As the thickness of the coating decreases ,the ther-mal fatigue resistance increases,The thermal fatigue resistance cuts down with the thermal cyclic upper temperature rising,The crack growth rate decreases with the increase in cyclic number until crack arrests.Thermal fatigue failure was not found along the interface of the coating/matrix.The tract of thermal fatigue crack cracks along the interfaces of phases.     

Effects of In-situ and Ex-situ Heat-Treatment Procedures on?the?Transport Properties of the MgB2 Superconducting Thin Films Fabricated by Ultrasonic Spray Pyrolysis (USP) System

Superconducting MgB₂ thin films have been prepared using Ultrasonic Spray Pyrolysis (USP) system. 2.4 MHz USP system and various solutions which contain different Mg, B and de-ionized water and LAPSA concentrations and gas atmospheres were used to obtain 500 nm to 1.0 ??m thick MgB₂ films. Some of the films produced were heat treated in-situ in the spraying chamber during deposition and some of them were annealed ex-situ in the tube furnace under Mg vapor. T _c and T _zero of the samples were obtained to be 39.5 K and 37.4, 39.5 and 37.0 for ex-situ and in-situ prepared films, respectively. The highest critical current density was obtained to be 4.12×10⁶ A?cm^?2 for ex-situ annealed films and 4.01×10⁶ A?cm^?2 for in-situ produced films. The result obtained indicated that the ex-situ preparation method provides improvement in the transport and magnetic properties.     

Effect of Powder Particle Shape on the Properties of In Situ Ti–TiB Composite Materials Produced by Selective Laser Melting

This work studied the preparation of starting powder mixture influenced by milling time and its effect on the particle morphology(especially the shape) and, consequently, density and compression properties of in situ Ti–Ti B composite materials produced by selective laser melting(SLM) technology. Starting powder composite system was prepared by mixing 95 wt% commercially pure titanium(CP-Ti) and 5wt% titanium diboride(TiB 2) powders and subsequently milled for two different times(i.e. 2 h and 4 h).The milled powder mixtures after 2 h and 4 h show nearly spherical and irregular shape, respectively.Subsequently, the resultant Ti–5 wt% TiB 2 powder mixtures were used for SLM processing. Scanning electron microscopy image of the SLM-processed Ti–Ti B composite samples show needle-shape TiB phase distributed across the Ti matrix, which is the product of an in-situ chemical reaction between Ti and TiB 2during SLM. The Ti–Ti B composite samples prepared from 2 h and 4 h milled Ti–TiB 2 powders show different relative densities of 99.5% and 95.1%, respectively. Also, the compression properties such as ultimate strength and compression strain for the 99.5% dense composite samples is 1421 MPa and 17.8%, respectively, which are superior to those(883 MPa and 5.5%, respectively) for the 95.1% dense sample. The results indicate that once Ti and TiB 2 powders are connected firmly to each other and powder mixture of nearly spherical shape is obtained, there is no additional benefit in increasing the milling time and, instead, it has a negative effect on the density(i.e. increasing porosity level) of the Ti–Ti B composite materials and their mechanical properties.     

Composite NiB–Graphite and NiB–PTFE Surface Coatings Deposited by the Dynamic Chemical Plating Technique

Dynamic chemical plating (DCP) is an alternative for producing metallic deposits on nonconductive materials and can be considered as a modified electroless coating process. This article describes the formation of composite NiB–particle films by the DCP technique. The particles used were micrometric graphite (1–2 µm) or PTFE (50–500 nm). The conditions for production of these coatings are presented along with the deposition rates, surface morphology, friction properties, and the degree of particle incorporation into the films.     

Local Structure of Fe–Cr Powders Prepared by Mechanical Alloying

We have studied the structure of Fe–Cr alloys prepared by mechanical alloying. According to X-ray diffraction data, all of the alloys are single-phase and consist of a BCC solid solution. The local structure of the alloys has been studied by Mössbauer spectroscopy. Analysis of the local environment of the Fe atoms leads us to assume clustering processes in the alloy containing 20 at % Cr and suggests that the alloys containing 35 and 50 at % Cr experience phase separation into regions of a homogeneous disordered chromium- enriched solid solution and an iron-enriched imperfect structure containing a considerable amount of dissolved gases.