Effect of sintering temperature on microstructures and mechanical properties of ZK60 magnesium alloys

In this study, ZK60 Mg alloys were prepared via hot-press sintering under a constant pressure of 30 MPa as well as Ar atmosphere. The sintering temperature was determined to be in the range of 450–600 °C with an interval of 50 °C. The effect of sintering temperature on the microstructures and mechanical properties of the alloys was investigated. All the four sintered alloys mainly exhibited an α-Mg-phase structure and equiaxed grain microstructure. However, a specific amount of melt, enriched in Zn element, formed when the sintering temperature reached 500 °C. Thus, only the alloy sintered at 450 °C maintained the nominal composition of the alloy powder, and exhibited the favorable yield strength and hardness, which was 135.1 MPa and 57 HV, respectively. The alloys sintered at 550 °C and 600 °C exhibited a reduced yield strength and hardness due to the loss of Zn element.

Determination of Porosity in Fluidized-Bed Carburized P/M Compacts Using an Image Software Analysis

The aim of this research was to study the porosity in carburizing in fluidized-bed on sintered alloys produced by powder metallurgy route using an image analysis software and to compare the obtained results with the conventional method for porosity measurements. Porosity is a measure of the void fraction in a material. The total porosity is defined by the ratio of the volume of void space to the total bulk volume of the material, expressed as a percentage. Development of digital images and computer software lead to a new and suitable method to determine the porosity of powder metallurgy materials.

Enhancement of the Mechanical and Tribological Properties of Aluminum-Based Alloys Fabricated by SPS and Alloyed with Mo and Cr

Multicomponent aluminum-based alloys doped with chromium (Cr) and molybdenum (Mo), fabricated by spark plasma sintering (SPS), derived from a powder mixture prepared by mechanical alloying, were studied in this work. The morphology of the pristine and worn surfaces was analyzed using a scanning electron microscope equipped with an energy-dispersive X-ray spectroscopy system. The obtained alloys exhibited higher hardness (73 and 72) for the Al–Mo and Al–Cr alloys, respectively, compared to reference bronze. Besides improved hardness, SPS-sintered alloys also showed a lower value of the weight and linear wear and the highest score-resistance compared to bronze. The enhanced tribological behavior is related to the formation of secondary structures on the friction surfaces of rubbing pairs, which in turn reduce wear. For the first time, the present research has demonstrated the effectiveness of the addition of Mo and Cr for the fabrication of sintered multicomponent Al-based alloys with a tailored microstructure that induces the formation of secondary structures on the tribosurfaces due to the self-organization processes during friction.

Microstructure and Sintering Behaviors of Al–Cr–xSi (at.%) System Alloys Processed by Spark Plasma Sintering

In this study, microstructure and sintering behaviors of the gas-atomized Al-(25 or 30) Cr–xSi alloy (x = 5, 10 and 20 at.%) during spark plasma sintering (SPS) process were investigated. Gas-atomized alloy powders were manufactured using Ar gas atomizer process. These alloy powders were consolidated using SPS process at different temperature under pressure 60 MPa in vacuum. Microstructures of the gas-atomized powders and sintered alloys were analyzed using scanning electron microscopy (SEM) with energy–dispersive X-ray spectrometer (EDS), and transmission electron microscopy (TEM). Hardness of the SPS sintered alloys was measured using micro Vickers hardness tester. The Al–Cr–Si bulks with high Cr and Si content were produced successfully using SPS sintering process without crack and obtained fully dense specimens close to nearly 100% T. D. (Theoretical Density). The maximum values of the hardness were 834 Hv for the sintered specimen of the gas atomized Al–30Cr–20Si alloy. Enhancement of hardness value was resulted from the formation of the multi-intermetallic compound with the hard and thermally stable phases and fine microstructure by the addition of high Cr and Si.

Effect of mechanical activation of WC-based powder on the properties of sintered alloys

Introduction. For the manufacture of wearproof tools and machine elements, the method of powder metallurgy is widely used. The preliminary high-intensity mechanical activation of the powder is used to improve the structure and properties of the alloy obtained by the method of powder metallurgy. The mechanical activation can result in formation of nanostructures with subsequent amorphization of the material, can bring phase transformations, it can certainly affect the properties of the material. However, mechanical treatment does not always lead to a positive result. Therefore, the study of the effect of mechanical activation of WC-based powder on the properties of sintered alloys is important. Purpose of the work: to study the effect of high-intensity mechanical activation of WC-based powder on the structure and properties of sintered samples. The work investigates alloys obtained by the method of powder metallurgy, using mechanically activated powders for 10 to 300 seconds in a planetary ball mill. Materials and methods. The alloys are obtained by cold one-sided pressing followed by sintering at a temperature of 1400 °C in a vacuum furnace. Particle morphology of powder and structure of alloys is analyzed by scanning electron microscopy method. The metallographic analysis of the alloys is carried out by optical microscopy. Phase analysis and the parameters of the crystal structure are performed by X-ray diffraction. The hardness of the sintered samples is measured by hardness tester. Results and its discussion. It is shown that after sintering of powders alloys with WC and Co phases are formed. The lattice parameter of the WC-phase correlates well with values in literature. A second carbide phase, Co3W3C, is formed in the samples upon mechanical activation for more than 100 sec. The minimum porosity of sintered sample is 7.8 ± 1 % that corresponds of sample with preliminary mechanical treatment for 30 seconds. It is shown that the hardness depends on grain size, porosity and second carbide content. Thus, mechanical activation can be effective for increasing the physical and mechanical properties and inhibiting grain growth, but in this case, it is necessary to carry out mechanical processing in the mechanical treatment time range 60-100 sec.

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).

Microstructure and mechanical characteristics of Cu-12.5Ni-5Sn-xFe sintered alloys

The Cu-12.5Ni-5Sn-xFe alloys were prepared using powder metallurgy. The effect of the amount of Fe addition on the microstructure and mechanical characteristics of Cu-12.5Ni-5Sn-xFe alloys was investigated. The microstructure and morphology of alloys were examined by means of X-ray diffraction, scanning electron microscopy and cold field emission scanning electron microscope. Results indicate that the hardness and yield strength of the Cu-12.5Ni-5Sn alloy are improved by addition of trace amounts of Fe. The lamellar precipitates of Cu-12.5Ni-5Sn-xFe alloys are more and finer compared to those of Cu-12.5Ni-5Sn alloy. Fe can facilitate the aging process and strengthen the effect of aging-hardening.

Compaction and Heat Treatment Effects on the Structural and Mechanical Properties of Sintered Fe3C-W-Co Alloys

In this article, the 75Fe3C-20W-5Co alloy is developed by the powder metallurgy technique in order to study the microstructure and the mechanical properties obtained after solid phase sintering. The mechanical grinding of the mixture of these Fe3C-W-Co powders lasted 6 hours.The powders were compressed by cold isostatic pressing (CIP) at different compaction pressures (5MPa, 10MPa, 15MPa and 18MPa). The green compacts obtained were sintered at a temperature equal to 1350 °C, followed by a heat treatment at different temperatures (850 °C, 950 °C and 1100 °C). The samples were then cooled in different baths (oil and water). The characterization of this sintered steel alloy was carried out by X-ray diffraction (XRD) and with an optical microscope. The results reveal that the structure of these sintered alloys consisted of the Fe matrix phase and the W-Co solid solution phase. The compaction pressure influences the number and size of the pores. Hardness and wear resistance increase with increasing compaction pressure.

Effect of silicon on the properties of sintered alloys of (Al – Si) – Sn system

Structural features of composites of the (Al – xSi) – 40Sn system prepared by liquid-phase sintering of mixtures of tin powder of PO 2 grade with powders of Al – Si alloys of hypoeutectic, eutectic, and hypereutectic composition were studied in this work. Samples were cut from the prepared materials for compression test and dry friction test against steel according to the “pin-on-disk” scheme. It was established that the main structural elements of the sintered composites are determined by the nature of interaction of solid silumin particles and liquid tin. This is due to the fact that tin not only spreads over the volume of the sintered compact, but also activates the processes of recrystallization of aluminum powders due to dissolution of their atoms in the liquid phase with subsequent deposition on the large particles surface. The dissolution weakens the skeleton of aluminum powders, and they are able to regroup into a denser configuration under the action of capillary forces. It was found that silicon inhibits the shrinkage of the compacts during the liquid-phase sintering. Therefore, to improve the mechanical properties of the sintered composites, they should be subjected to additional densification in order to eliminate their residual porosity, which simultaneously contributes to a significant increase in their wear resistance under dry friction. The study of the wear features of the (Al – хSi) – 40Sn composites was carried out. It was found that silicon particles located in the tin interlayers hinder the relative shear of the neighboring matrix grains and increase the thickness of the surface layer involved in deformation by friction forces. This fact has a favorable effect on the wear resistance of the investigated sintered composites under dry friction process. The (Al – 12Si) – 40Sn composite sample with the eutectic matrix has the highest wear resistance.