Does Simulated Porcelain Firing Influence Corrosion Properties of Casted and Sintered CoCr Alloys?

The aim of the study was to evaluate how heat processing used for dental porcelain firing influences the surface properties of sintered and casted CoCr alloy. Two CoCr alloys, Soft Metal LHK (milling in soft material and sintering) and MoguCera C (casting), were used for the study. The samples were examined using SEM–EDS before and after heat treatment. Next, corrosion examinations (Ecorr, jcorr, polarization curve, Ebr) were performed. Finally, the samples were evaluated under SEM. Based on the results, the following conclusions might be drawn: 1. Thermal treatment (porcelain firing) did not cause chemical impurities formation on the surface of CoCr alloy; 2. The sintered metal exhibited significantly higher corrosion resistance than the casted one due to its homogeneity of structure and chemical composition; 3. Heat treatment (porcelain firing) decreased the resistance of casted and sintered CoCr alloy to electrochemical corrosion. The reduction in corrosion resistance was significantly higher for the casted alloy than for the sintered alloy; 4. The corrosion resistance decrease might be due to an increased thickness and heterogeneity of oxide layers on the surface (especially for the casted alloy). The development of corrosion process started in the low-density areas of the oxide layers; 5. The sintered metal seems to be a favourable framework material for porcelain fused to metal crowns.

Effect of Microwave and Conventional Modes of Heating on Sintering Behavior, Microstructural Evolution and Mechanical Properties of Al-Cu-Mn Alloys

In this research, we intended to examine the effect of heating mode on the densification, microstructure, mechanical properties, and corrosion resistance of sintered aluminum alloys. The compacts were sintered in conventional (radiation-heated) and microwave (2.45 GHz, multimode) sintering furnaces followed by aging. Detailed analysis of the final sintered aluminum alloys was done using optical and scanning electron microscopes. The observations revealed that the microwave sintered sample has a relatively finer microstructure compared to its conventionally sintered counterparts. The experimental results also show that microwave sintered alloy has the best mechanical properties over conventionally sintered compacts. Similarly, the microwave sintered samples showed better corrosion resistance than conventionally sintered ones.

Femtosecond Laser Trimming with Simultaneous Nanostructuring to Fine Piercing Punch to Electrical Amorphous Steel Sheets

A CVD (Chemical Vapor Deposition) diamond coated tungsten carbide (WC) and cobalt (Co) sintered alloy punch was trimmed by the femtosecond laser machining to sharpen its edge with about 2 μm and to simultaneously make nanostructuring to its side surface. In addition to the sharpened edge, its edge profile was formed to be homogeneous enough to reduce the damage layer width by piercing the electrical amorphous steel sheet stack. Each brittle sheet in the stacked work was damaged to have three kinds of defects by piercing; e.g., the droop-like cracking in the thickness and at the vicinity of hole, the wrinkling in peak-to-valley with partial cracking on the peaks, and the circumferential cracking. When using the WC (Co) punch with the inhomogeneous edge profile in the sharpened edge width, these three damages were induced into each sheet and the maximum damage width exceeded 80 μm. When using the punch with the sharpened edge and homogeneous edge profile, the wrinkling mode was saved and the total affected layer width was significantly reduced to less than 20 μm. Through the precise embossing experiments, this effect of punch edge profile condition to the induced damages was discussed with a statement on the nanostructuring effect on the reduction of damaged width in electrical amorphous steel sheets. The developed tool with the sharpened edge and homogenous edge condition contributes to the realization of a low iron loss motor with a reduced affected layer width.

Production of gradient ultrafine-grained hard alloys from powders obtained from scrap VK15 alloy dispersed in water and scrap VK8 alloy dispersed in oil

An experiment has been carried out aimed at producing a low-cost tool material which would have an extra hard surface and a crack resistant base phase. A double-layer gradient alloy was produced out of powders with excessive and insufficient carbon obtained from alloys VK8 and VK15 by electrospark dispersion. To obtain the initial powder, plates of the VK8 alloy scrap material initially containing 5.6% of carbon were dispersed in oil. This caused excessive carbon (3.1%), which was then partially reduced to 0.6% by CO2 heat treatment. The VK15 alloy with 5.3% of initial carbon was dispersed in water to achieve an insufficient carbon concentration (2.8 %) in it. It was then heat treated in the CO atmosphere to partially lower the carbon concentration to 0.7%. The dispersed powder was found to consist of spherical microparticles, as well as agglomerated nanoparticles obtained through crystallization of liquid and vapour phases. Mixing of tungsten and cobalt phases resulted in much smaller diameters of WC grains in the newly sintered alloy. This combination of deviations in the carbon concentration between the layers helped maintain the unequal concentration of cobalt (8 and 15%) and thus ensure an extra hard surface (1820HV) and a crack resistant base (14.2 MPa√m). Analysis was carried out to estimate the power costs, as well as the performance of the laboratory unit used for electrospark dispersion of hard alloys.

Influence of Nickel Powder Particle Size on the Microstructure and Densification of Spark Plasma Sintered Nickel-Based Superalloy

This study aims to investigate the effects of powder particle size on the densification and microhardness properties of spark plasma sintered superalloy. Three particles size ranges of nickel were used in this study, namely, (3-44, 45-106 and 106-150 μm), and this is the matrix in the IN738LC superalloy composition (powder), used in the study. The effects of the particle size were examined at a specific applied temperature and pressure. The transitioning stages during the sintering process of the green powders to the formation of the sintered alloy were analyzed and given as the particle rearrangement stage, the localized deformation stage and the neck formation/grain growth stage. There was the formation of γ, γ' and a solid solution within the microstructure of the sintered alloys. The effect of particle size was more pronounced on the grain sizes obtained, while the phases formed is the same for the three alloys. The results indicate that the nickel particle size (>60% of the total composition) has a significant influence on the densification, porosity, grain size and hardness properties of the IN738LC sintered alloy. Finer nickel particle size resulted in a sintered product with smaller grain size (9 µm), reduced percentage porosity (3.9%), increased relative density (96.1%) and increased hardness properties (371 Hv).

Thermomechanical Processing of Cost-Affordable Powder Metallurgy Ti-5Fe Alloys from the Blended Elemental Approach: Microstructure, Tensile Deformation Behavior, and Failure

The development of cost-affordable Ti alloys is key for the application of Ti in other industries like the automobile sector. Therefore, a combination of powder metallurgy (PM) and low-cost compositions is an interesting approach. In this article, a cost-affordable PM Ti-5Fe alloy is processed following the blended elemental route and extruded at high temperature to remove porosity. Different extrusion temperatures and heat treatments (i.e., solution treatment and aging, STA) are performed to obtain ultrafine microstructures, and their effect on the mechanical behavior is studied. For extrusions in the β phase, microstructures consist of coarse lamellar colonies, resulting in alloys with improved properties compared to the as-sintered alloy but still lacking toughness due to the failure happening just after necking onset. Extruding in the α + β phase results in a bimodal microstructure of fine elongated primary α and coarse lamellar colonies, and the alloy becomes tougher. STA with aging below the eutectoid temperature of 590 °C leads to a hard but brittle alloy, whereas STA with aging above it results in alloys with strength comparable to the as-extruded conditions and enhanced ductility.

Titanium-Based Sintered Alloy with Improved Wear Resistance

Titanium sintered alloys have a special use in the technique because they have multiple advantages. Titanium and its alloys are characterized by remarkable physic-chemical, mechanical and technological properties. However, there are several such properties that have a lower value, such as friction behavior. Titanium and its alloys are recognized as having low wear resistance. Titanium alloyed with certain elements, such as tin or graphite, can lead to alloys with improved wear properties, with the specification that graphite does not exceed 1%. The technology of manufacturing titanium-based alloys is specific to powder metallurgy, but it also has some originality by choosing special sintering cycles. The paper aims to present a tribological characterization of the sintered TiAl alloy; the method uses the disc of the alloy that has been researched in contact with an alumina ball. The paper presents a detailed analysis of the wear tests carried out for four types of specimens obtained by different methods.

The in situ redispersion of a PdCu/AC alloy catalyst under a CFCl2CF2Cl/H2 atmosphere: a combination of experimental and DFT study

A novel CFCl2CF2Cl(R113)/H2 gas treatment process was proposed and successfully applied for the redispersion of a sintered alloy PdCu/AC catalyst.