Powder Metallurgy Samples Research Articles

Using fused filament fabrication to improve the tribocorrosion behaviour of 17-4 PH SS in comparison to other metal forming techniques

Fused filament fabrication (FFF) is one of the additive manufacturing processes which has gained more interest because of its simplicity and low-cost. This technology is similar to the conventional metal injection moulding (MIM) process, consisting of the feedstock preparation of metal powder and polymer binders, followed by layer-by-layer 3D printing (FFF) or injection (MIM) to create green parts and, finally, debinding and sintering. Moreover, both technologies provide near-dense parts. This work presents an in-depth study of the processing method’s influence. The porosity, microstructure, hardness, corrosion, and tribocorrosion behaviour are compared for 17-4 PH SS samples processed from powder by additive manufacturing using FFF and MIM, as well as conventional powder metallurgy (PM) samples. MIM samples exhibited the highest macro and microhardness, while corrosion behaviour was similar for both MIM and FFF samples, but superior in comparison to conventional PM samples. However, the FFF-as fabricated samples displayed a significant improvement in tribocorrosion resistance that could be explained by the higher proportion of delta ferrite and retained austenite in their microstructure.

Microstructure and mechanical properties of Ti-Nb alloys: comparing conventional powder metallurgy, mechanical alloying, and high power impulse magnetron sputtering processes for supporting materials screening

At the interface of thin film development and powder metallurgy technologies, this study aims to characterise the mechanical properties, lattice constants and phase formation of Ti-Nb alloys (8–30 at.%) produced by different manufacturing methods, including conventional powder metallurgy (PM), mechanical alloying (MA) and high power impulse magnetron sputtering (HiPIMS). A central aspect of this research was to investigate the different energy states achievable by each synthesis method. The findings revealed that as the Nb content increased, both the hardness and Young’s modulus of the PM samples decreased (from 4 to 1.5 and 125 to 85 GPa, respectively). For the MA alloys, the hardness and Young’s modulus varied between 3.2 and 3.9 and 100 to 116 GPa, respectively, with the lowest values recorded for 20% Nb (3.2 and 96 GPa). The Young’s modulus of the HiPIMS thin film samples did not follow a specific trend and varied between 110 and 138 GPa. However, an increase in hardness (from 3.6 to 4.8 GPa) coincided with an increase in the β2 phase contribution for films with the same chemical composition (23 at.% of Nb). This study highlights the potential of using HiPIMS gradient films for high throughput analysis for PM and MA techniques. This discovery is important as it provides a way to reduce the development time for complex alloy systems in biomaterials as well as other areas of materials engineering.Graphical abstract

The Mechanical Properties of Aluminum Metal Matrix Composites Processed by High-Pressure Torsion and Powder Metallurgy.

Al-Al2O3 and SiC metal matrix composites (MMCs) samples with different volume fractions up to 20% were produced by high-pressure torsion (HPT) using 10 GPa for 30 revolutions of Al-Al2O3, and SiC and powder metallurgy (PM). The effect of the processing method of micro-size Al MMCs on the density, microstructure evolution, mechanical properties, and tensile fracture mode was thoroughly investigated. HPT processing produces fully dense samples relative to those produced using powder metallurgy (PM). The HPT of the Al MMCs reduces the Al matrix grain size and fragmentation of the reinforcement particles. The Al matrix average grain size decreased to 0.39, 0.23, and 0.2 µm after the HPT processing of Al, Al-20% Al2O3, and SiC samples. Moreover, Al2O3 and SiC particle sizes decreased from 31.7 and 25.5 µm to 0.15 and 0.13 µm with a 99.5% decrease. The production of ultrafine grain (UFG) composite samples effectively improves the microhardness and tensile strength of the Al and Al MMCs by 31-88% and 10-110% over those of the PM-processed samples. The good bonding between the Al matrix and reinforcement particles noted in the HPTed Al MMCs increases the strength relative to the PM samples. The tensile fracture surface morphology results confirm the tensile properties results.

Microstructural Development of Ti-6Al-4V Alloy via Powder Metallurgy and Laser Powder Bed Fusion

A detailed study was carried out to gain a better understanding of the microstructural differences between Ti-6Al-4V parts fabricated via the conventional powder metallurgy (PM) and the laser powder bed fusion (L-PBF) 3D printing routes. The parts were compared in terms of the constituent phases in the microstructure and their effects on the micro- and nano-hardness. In L-PBF parts, the microstructure has a single phase of martensitic α′ with hcp crystal structure and acicular laths morphology, transformed from prior parent phase β formed upon solidification of the melt pool. However, for the sintered parts via powder metallurgy, two phases of α and β are noticeable and the microstructure is composed of α grains and α + β Lamellae. The microhardness of L-PBF processed Ti-6Al-4V samples is remarkably higher than that of the PM samples but, surprisingly, the nano-hardness of the bulk martensitic phase α′ (6.3 GPa) is almost the same as α (i.e., 6.2 GPa) in PM samples. This confirms the rapid cooling of the β phase does not have any effect on the hardening of the bulk martensitic hcp α′. The high microhardness of L-PBF parts is due to the fine lath morphology of α′, with a large concentration of low angle boundaries of α′. Furthermore, it is revealed that for the α phase in PM samples, a higher level of vanadium concentration lowers the nano-hardness of the α phase. In addition, as expected, the compacting pressure and sintering temperature during the PM process led to variations in the porosity level as well as the microstructural morphology of the fabricated specimens, which will in turn have a significant effect on the mechanical properties.

Study of dry wear behavior of Novel ferrous samples prepared by powder metallurgy method

The sliding wear behavior of newly developed ferrous powder metallurgy samples was investigated under dry sliding conditions. Wear tests were conducted by varying the normal loads of 30 N, 40 N, and 50 N at a constant velocity of 1 m s−1 and then at a constant load of 30 N by varying the sliding velocities by 0.5 m s−1, 1 m s−1, and 2 m s−1 at room temperature. Furthermore, the variations in the wear rate and coefficient of friction at a constant sliding distance of 5400 m were studied at different normal loads keeping sliding velocity constant at 1 m s−1 as well as at different sliding velocities and maintaining normal load at 30 N. The wear characteristics were evaluated using weight loss measurements. The mechanism of wear was observed using a scanning electron microscope and compositional analysis using energy-dispersive X-ray spectroscopy (EDX). It was found that increased normal load had a dominant effect on the wear loss in comparison to increased sliding speed during the tribological testing of the powder metallurgy samples.

An overview on the microstructure and mechanical properties of sintered aluminum-based composites

Sintered composites have revolutionized as a thermal treatment to consolidate a wide range of engineering materials where the transition of powders takes place thermally in a thermodynamical equilibrium state with a decrease in free surface energy in materials owing to their specific capability. Sintering aids in providing effective bonding between the reinforced powder particles. However, the inadequate understanding of the sintering mechanism may limit the practical application of a few materials such as aluminum metal matrix composites. In addition to the rapid growth of various sintering related technologies, researchers need attention to highlight the structural barriers and forecast the emerging demands while dealing with such composites. A review report is made in this paper regarding the sintering mechanisms and sintering techniques. Common sintering techniques such as traditional, microwave assisted, hot pressing, hot isostatic sintering, and spark plasma sintering are identified and discussed here. As a result, the key challenges in sintering aluminium metal matrix composites that can affect sintering parameters are investigated. From the review, spark plasma is identified to attain densified and pore-free green composites and, microwave sintering is the best technique for achieving uniform microstructure in powder metallurgy samples.

Sifat Mekanik Produk Metalurgi Serbuk dari Proses Ball Milling dengan Bahan Baku Al7075 Terhadap Variasi Temperatur Sinter dan Tekanan Kompaksi

Powder metallurgy samples, made from Al7075 powder from ball milling, were produced and investigated. Samples were subjected to two different variables, those were compaction pressure and sintering temperatur. Compaction pressure variables were 250, 300, and 350 MPa with constant sintering temperatur of 505oC. Sintering temperatur variations were 425, 465, and 505oC with constant compaction pressure of 350 MPa. The results of density measurement and hardness test were directly proportional to both of research variables, whereas the porosity was inversely proportional. The properties of sample with variables of 350 MPa compaction pressure and 505oC sintering temperatur were the closest one to conventional Al7075, with density of 2.173 g/cm3, 22.2% porosity, and 12.56 VHN hardness. The properties of conventional Al7075 sample were 2.8 g/cm3 density, 0.26% porosity, and 12.68 VHN hardness. The abrupt increase of hardness between 465oC and 505oC sintering temperatur was similar in pattern of its porosity decrease. This means optimum porosity decrease was started between 465oC and 505oC which affecting hardness increase. Highest hardness of powder metallurgy Al7075, which was 99% of conventional Al7075 and porosity of 22.2%, suggested wide application potential of Al7075 produced by powder metallurgy.

Comparison of Cu–Al–Ni–Mn–Zr shape memory alloy prepared by selective laser melting and conventional powder metallurgy

Abstract This work aimed to investigate and critically analyze the differences in microstructural features and thermal stability of Cu−11.3Al−3.2Ni−3.0Mn−0.5Zr shape memory alloy processed by selective laser melting (SLM) and conventional powder metallurgy. PM specimens were produced by sintering 106−180 µm pre-alloyed powders under an argon atmosphere at 1060 °C without secondary operations. SLM specimens were consolidated through melting 32−106 µm pre-alloyed powders on a Cu−10Sn substrate. Mechanical properties were measured through Vickers hardness testing. Differential scanning calorimetry was conducted to assess the martensitic transformation temperatures. X-ray diffraction patterns were collected to identify the metallurgical phases. Optical and scanning electron microscopy was used to analyze the microstructural features. β′1 martensite was found, irrespective of the processing route, although coarser martensitic variants were present in PM-specimens. In conventional powder metallurgy samples, intergranular eutectoid constituents and stabilized austenite also formed at room temperature. PM-specimens showed similar average hardness values to the SLM-specimens, albeit with high standard deviation linked to the porosity. The specimens processed by SLM showed reversible martensitic transformation (T0=171 °C). PM-processed specimens did not show shape memory effects.

Cryogenic mechanical alloying of aluminum matrix composites for powder bed fusion additive manufacturing

Cryogenic mechanical alloying (cryomilling) was employed to fabricate aluminum matrix composite powder feedstock for additive manufacturing. The high energy milling of the powder system induces a homogenous distribution of reinforcement particles in the matrix powder by recurrent fracture and cold welding. In this study, aluminum matrix composite feedstock were produced via different cryomilling techniques at varying compositions, powder charges, and milling times. As-milled powders were characterized for particle size distribution, morphology, and homogeneity. Resultant powder demonstrated varying characteristics correlated to milling parameters. Powder metallurgy samples were also fabricated to understand as-sintered reinforcement distribution and the resultant strengthening. This research provides an indication of cryomilling capabilities to become an effective method for custom alloy powder production for powder bed fusion additive manufacturing.

Additively Manufactured Al/SiC Cylindrical Structures by Laser Metal Deposition.

Preliminary characterization of the microstructure of Al/SiCp composites prepared by Laser Metal Deposition (LMD) was analyzed, and the microhardness and wear behavior of the materials manufactured have been evaluated. It has been determined that the combined effect of the laser speed and power is decisive for the fabrication process. The microstructure characterization shows that the presence of hygroscopic Al4C3 can be avoided by adding Ti to the composite matrix. The wear behavior of the LMD samples and their microhardness have been compared with Powder Metallurgy samples with the same composition. The LMD samples showed higher hardness and wear resistance.

Properties of a rapidly solidified Ni–Nb layer prepared using a high-current pulsed electron beam

In this study, the surface of a bulk crystalline Ni–Nb powder metallurgy (PM) sample of a glass-forming composition was investigated using high-current pulsed electron-beam (HCPEB) irradiation, which also improved the surface properties. Unlike the original crystalline sample, X-ray diffraction (XRD) of the surface shows an amorphous phase following HCPEB exposure. Transmission electron microscopy (TEM) reveals that, after the Ni–Nb PM samples were exposed to 20 or 30 pulses of HCPEB irradiation, the re-melted layer contains localized nanocrystalline regions within an amorphous matrix. The scanning electron microscopy (SEM) results indicate that, after 30 pulses, a re-melted layer about 5 μm in thickness forms on the surface of the Ni–Nb PM samples. Meanwhile, a large number of cracks and craters were observed on the re-melted layer. In addition, the micro-hardness tests reveal that the micro-hardness improves significantly after HCPEB irradiation. The microhardness of the sample was the highest after the 30 pulses, which was 1.5 times that of the original sample. Furthermore, potentiodynamic polarization tests indicate that the irradiated samples of corrosion resistance were not enhanced compare to the initial samples, due to the formation of cracks providing a Cl− etching channel that accelerates the corrosion rate.

Electrochemical Behavior of Alumix 321 PM and AA6061 Alloys in 3.5 wt% NaCl Solution by Electrochemical Impedance Spectroscopy Measurements

Powder metallurgy (PM) is a very interesting metal manufacturing technique in the production of automotive components of a net or near net shape. In this research, the electrochemical corrosion behavior of a commercially available aluminum powder alloy known as Alumix 321 was investigated and compared to wrought alloy AA6061 in 3.5 wt% NaCl solution using Electrochemical Impedance Spectroscopy Measurements (EIS). Alumix 321 alloy samples were prepared by pressing the powder at pressures ranging from 50 to 500 MPa and subsequently sintering them for 30 min at 630°C. It was found that the presence of pores and their morphology strongly affect the corrosion behavior the PM samples.

In situ detection of thermally induced porosity in additively manufactured and sintered objects

Dilatation measurements, combined with thermal programmed desorption mass spectrometry (TPD-MS), were utilized for studying thermally induced porosity (TIP) in selective laser melting additively manufactured (AM) AlSi10Mg and Ta30at.%–Ti samples produced by hot isostatic pressing (HIP). A clear abrupt upward deviation in thermal expansion is observed, most probably indicating the occurrence of TIP mechanisms in both AM objects and powder metallurgy samples. For both AlSi10Mg and Ta30at.%–Ti, pores are clearly observed by either microscopic or macroscopic examinations. The TPD-MS analysis shows that both water and hydrogen evolve from AlSi10Mg powder particles, thus suggesting that thermally induced expansion of trapped hydrogen in HIP’ed Ta30at.%–Ti alloy and in laser powder bed fusion AlSi10Mg is the main source for the pressure increase in pores that consequently leads to permanent expansion upon heating. A simplified model that correlates the pressure inside the pores with the weakening of the material upon heating and TIP is proposed.

Effect of the fabrication method on the wear properties of copper silicon carbide composites

Abstract The wear properties of copper and copper silicon carbide composites processed by powder metallurgy (PM) and high-pressure torsion (HPT) under different sliding distances and applied loads by using dry reciprocated sliding wear test were investigated. HPT improves wear resistance obviously not only relative to PM samples and but also to results previously noted for different Cu composites. The grain refinement with the formation of bimodal and trimodal microstructures after HPT processing improves the wear properties. Wear mechanism depends mainly on material processing method, it converted from adhesive, delamination in the case of PM samples into abrasive wear after HPT. X-ray spectroscopy (EDS) analysis and surface morphology observations of the worn samples and WC ball prove and support the wear results.

Thermal Stability of Zone Melting p-Type (Bi, Sb)2Te3 Ingots and Comparison with the Corresponding Powder Metallurgy Samples

During the past few decades, Bi2Te3-based alloys have been investigated extensively because of their promising application in the area of low temperature waste heat thermoelectric power generation. However, their thermal stability must be evaluated to explore the appropriate service temperature. In this work, the thermal stability of zone melting p-type (Bi, Sb)2Te3-based ingots was investigated under different annealing treatment conditions. The effect of service temperature on the thermoelectric properties and hardness of the samples was also discussed in detail. The results showed that the grain size, density, dimension size and mass remained nearly unchanged when the service temperature was below 523 K, which suggested that the geometry size of zone melting p-type (Bi, Sb)2Te3-based materials was stable below 523 K. The power factor and Vickers hardness of the ingots also changed little and maintained good thermal stability. Unfortunately, the thermal conductivity increased with increasing annealing temperature, which resulted in an obvious decrease of the zT value. In addition, the thermal stabilities of the zone melting p-type (Bi, Sb)2Te3-based materials and the corresponding powder metallurgy samples were also compared. All evidence implied that the thermal stabilities of the zone-melted (ZMed) p-type (Bi, Sb)2Te3 ingots in terms of crystal structure, geometry size, power factor (PF) and hardness were better than those of the corresponding powder metallurgy samples. However, their thermal stabilities in terms of zT values were similar under different annealing temperatures.

Influence of Ingot and Powder Metallurgy Production Route on the Tensile Creep Behavior of Mo–9Si–8B Alloys with Additions of Al and Ge

Refractory metals and their alloys show potential for high temperature applications, due to the elevated melting points often paired with very good creep resistance. Spark plasma sintering (SPS) as well as arc‐melting is used here to prepare quaternary and quinternary Mo–9Si–8B–xAl–yGe (x is 0 or 2; y is 0 or 2, all numbers in at%) samples. All samples consist of a Mo solid solution (Moss) and two intermetallic phases: Mo3Si (A15) and Mo5SiB2 (T2). Aluminum and germanium reduce the melting point and slightly decrease the density of the material. The specimens are homogenized and coarsened by a subsequent heat‐treatment in vacuum at 1850 °C for 24 h. The resulting microstructure is investigated using scanning electron microscope (SEM), energy‐dispersive X‐ray spectroscopy (EDS), X‐ray diffraction (XRD), X‐ray fluorescence spectroscopy (XRF), and inductively coupled plasma optical emission spectrometry (ICP‐OES) analysis. A vacuum creep testing device for small tensile creep specimens is presented. It is heated by graphite radiation heaters usable up to 1500 °C in vacuum of 2 · 10‐4 Pa with an oil diffusion pump. Tensile creep tests are performed at 1250 °C and stresses from 50 MPa up to 250 MPa. Specimens produced by ingot metallurgy feature superior creep properties compared to powder metallurgy samples.

A method to rapidly determine the sintering process parameters of powder metallurgy by real-time resistivity monitoring

A new method, which is called the resistivity method, is applied in this paper to explore the optimum sintering parameters of powder metallurgy (PM) since general methods are always labor-intensive and time-consuming. This method can probe the resistivity of the powder metallurgy samples in real-time during the sintering process, to quickly estimate the change of the relative density, which consequently determine the properties of the sintered item. As an example, in this paper, copper/tungsten carbide (Cu/WC) composites and pure aluminum (Al) powder compacts are experimentally considered. As a result, for the Cu/WC composites, the highest value of relative density appeared at the holding time of 50 min where the sample has the lowest resistivity. For the Al compacts, the optimum sintering temperature is 450 °C, and the longer the holding time the better.

Influence of Processing Procedure on Mechanical Properties of A319 by Comparison between Casting and Powder Metallurgy

Al-6wt.%Si-3.5wt.%Cu alloy (A319) were prepared by casting and powder metallurgy (PM) methods to investigate the influence of processing procedure on properties. The casting samples were cast into a horizontal mold after degassing by argon. The PM samples were extruded after hot-press sintering before which Al-11wt.%Si master alloy powder, pure Al powder and 48 h ball-milled Al-40wt.%Cu powder were blended for 12 h at rotation speed of 250rpm. The samples underwent a T6 temper, i.e. solution, water quenching and artificial aging. Microstructures were observed by optical microscope (OM) and scanning electron microscope (SEM), and phases were determined by X-ray diffraction (XRD). The tensile testing was carried out on universal testing machine. The results showed that heat treatment could greatly improve the tensile strength of the samples, especially for the casting counterpart. Discussion was made to analyze the reason that the properties differed.

Investigation of microstructure and mechanical properties of nano MgO reinforced Al composites manufactured by stir casting and powder metallurgy methods: A comparative study

In the present work, Al–nano MgO composites using A356 aluminum alloy and MgO nanoparticles (1.5, 2.5, and 5vol.%) have been fabricated via stir casting and powder metallurgy (PM) methods. Different processing temperatures of 800, 850, and 950°C for stir casting and 575, 600, and 625°C for powder metallurgy were considered. Powder metallurgy samples showed more porosity portions compare to the casting samples which results in higher density values of casting composites (close to the theoretical density) compare to the sintering samples. Introduction of MgO nanoparticles to the Al matrix caused increasing of the hardness values which was more considerable in casting samples. The highest hardness value for casting and sintering samples have been obtained at 850 and 625°C respectively, in 5vol.% of MgO. Compressive strength values of casting composites were higher than sintered samples which were majorly due to the more homogeneity of Al matrix, less porosity portions, and better wettability of MgO nanoparticles in casting method. The highest compressive strength values for casting and sintered composites have been obtained at 850 and 625°C, respectively. Scanning electron microscopy images showed higher porosity portions in sintered composites and more agglomeration and aggregation of MgO nanoparticles in casting samples which was due to the fundamental difference of two methods. Generally, the optimum processing temperatures to achieve better mechanical properties were 625 and 850°C for powder metallurgy and stir-casting, respectively. Moreover, casting method represented more homogeneous data and higher values of mechanical properties compare to the powder metallurgy method.

Bending Properties of Al-Steel and Steel-Steel Composite Metal Foams

The performance of new composite metal foams (CMFs) under bending was evaluated with simultaneous acoustic emission (AE) monitoring on samples processed by cast and powder metallurgy (PM) techniques. The results showed high maximum strength in all samples up to 86 MPa with more ductile failure in PM samples. Acoustic emission behavior confirmed that the dominating failure mechanism of cast CMF is the brittle fracture of intermetallic phases that mostly exist at the interface of the steel spheres with the aluminum matrix, whereas in PM samples (100 pct steel), the failure is governed by the propagation of preexisting microporosities in the matrix resulting in a complete ductile failure. SEM imaging of the fracture surfaces supported these findings.