Powder Metallurgy Alloys Research Articles

Workability and corrosion behavior studies on sintered iron‐based hybrid powder metallurgy alloys

AbstractSintered low carbon steels are developed using prealloyed and elemental powders to improve the mechanical properties of powder metallurgy and powder forged parts. The research focuses on the mechanism of workability and corrosion studies on sintered preforms of Alloy 1 (ATOMET4601 + 0.35%C) and Alloy 2 (ATOMET4601‐0.35%C‐0.25%Mn‐0.1%Si‐0.9%Cr). Sintered preforms of relative densities of 81%, 84%, and 90% were used for the present work. The preforms with 84% relative density have been used to study the formability parameters. It is observed from the experimental study that the Alloy 2 preforms with the addition of alloying elements have undergone lesser densification and deformation due to the work hardening mechanism. Corrosion studies have been carried out by conducting aqueous immersion and electrochemical corrosion tests on these two alloys using 18% HCl solution at different timings. It is found that the Alloy 2 has exhibited a better corrosion resistance than the Alloy 1 due to the addition of various alloying elements. It is also observed that the corrosion rate has decreased with an increase in densification irrespective of the alloys. The microstructures, scanning electron microscopy, and X‐ray diffraction of corroded surfaces have been corroborated with densification and the corrosion behavior of alloys.

Effect of Cr Addition on Properties and Tribological Behavior at Elevated Temperature of Boride Layers Grown on Borosintered Powder Metallurgy Alloys

Effect of Cr Addition on Properties and Tribological Behavior at Elevated Temperature of Boride Layers Grown on Borosintered Powder Metallurgy Alloys

Oxidation Characteristics of Nickel-Based Superalloy Powders Exposed at Ambient Condition

The existence of adsorbed oxygen and oxides on the surface of initial powders has serious effects on the microstructure and mechanical properties of the powder metallurgy alloys. However, the powder surface is inevitably oxidized immediately after the powder preparation. In this work, the oxidation characteristics for the argon atomized powders of a Ni-based superalloy containing Cr, Co, W, Mo, Nb, Ti and Al after exposure at ambient condition for various time were investigated in detail. It is found that various gases can be absorbed on the powder surface, but most of them can be removed by low temperature (<151.5 °C) outgassing procedure. The thermodynamic calculation shows that the oxidation reaction occurs firstly with the alloying elements rather than Ni matrix, whether at room temperature or elevated temperature. The kinetic measurement indicates that the oxygen content on the powder surface approaches a saturation value after 24 h exposure and remains almost stable after 720 h. The oxygen content increases with the decrease of particle size after exposure. X-ray photoelectron spectroscopy characterized that, except the formed oxides, adsorbed oxygen also exists on the powder surface of the as-atomized initial fine powders with particle size <30 μm and the powders with size >18.7 μm after exposure, which may be caused by the internal stress and surface energy of the initial atomized powder. All alloying elements except Ti can form stable oxides directly on the powder surface. For the element of Ti, the metastable TiO forms on the initial powder surface after preparation and it transforms into stable TiO2 or Ti2O3 during exposure. The results provide a deep understanding of absorbed gases and oxide on the surface of powders under treatment and possible desorption approach.

Effect of Eco‐Friendly Minimum Quantity Lubrication in Hard Machining of Vanadis 10: A High Strength Steel

Vanadis 10 SuperClean is a high vanadium alloyed powder metallurgy tool steel offering a unique combination of an excellent abrasive wear resistance in combination with a good chipping resistance. In this study, the effects of the eco‐friendly (100% biodegradable plant‐based) Minimum Quantity Lubrication (MQL) system on the cutting temperature, cutting tool vibration amplitude, tool wear, average surface roughness, and tool life in the turning of Vanadis 10 steel (50 HRC) used in the automotive industry are investigated. In the experiments, TiCN/Al2O3/TiN‐coated cemented carbide tools are used. Experimental results showed that, compared to Dry machining, MQL produced remarkable improvements in terms of cutting temperature, cutting tool vibration amplitude, tool wear, and surface roughness. In addition, the Taguchi experimental design, ANOVA, and linear and quadratic regression analyses are applied to the experimental data. The statistical analysis found the most effective parameter on average surface roughness to be the cutting environment (86.31%). It is determined that the cutting speed was the most effective on vibration amplitude and tool wear (46.22% and 32.41%). The correlation coefficients for the linear and quadratic regression analysis were 0.9 and 0.95, respectively.

Sinter-swage processing of an Al-Si-Mg-Cu powder metallurgy alloy

ABSTRACT A powder metallurgy (PM) alloy similar to wrought aluminum alloy 6013 was researched. Alloy variants emphasised systems with/without prealloyed manganese and admixed elemental tin powder. Systems with prealloyed manganese demonstrated an inferior response to die compaction and only achieved a density of 91% of theoretical after sintering. Conversely, the mixture that contained a trace addition of tin and was devoid of manganese densified to >98%. In the T6 state, this particular PM variant exhibited stiffness and yield strength that were comparable to wrought 6013-T6 but maintained a limited tensile ductility. The latter trait, as well as UTS and fatigue performance, were all improved significantly with the inclusion of a hot swaging step after sintering. As hot swaging eliminated the bulk of residual porosity in the sintered preform, this was believed to have underpinned much of the gains realised.

Electrochemical corrosion behavior of Ti–35Nb–7Zr–5Ta powder metallurgic alloys after Hot Isostatic Process in fluorinated artificial saliva

The present study aimed to evaluate the effect of the Hot Isostatic Process (HIP) process on the microstructure, phase stability and corrosion resistance of Ti35Nb7Zr5Ta powder metallurgy alloys. The corrosion resistance of titanium alloys was tested by analyzing the open circuit potential (OCP), potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and ion release in physiological Fusayama solution. Polarization curves showed that the Ti–35Nb–7Zr–2Ta alloy presented good passivation behavior thanks to its low current densities (<10−8 A/cm2) and high polarization resistance. The interpretation of an equivalent electric circuit (EEC) demonstrated the formation of a very stable oxide film on the alloy, as indicated by good capacitive behavior, high impedance values (>106 Ω cm2) at low frequencies and phase angles close to −90° according to the EIS results with less ion release.

Metastable Ti-Fe-Ge alloys with high elastic admissible strain

Iron is employed as an alloying element in powder metallurgy Ti alloys for healthcare applications owing to its fast diffusion which aids sintering, excellent biocompatibility, and cost-effectiveness. In this study, we assess the use of Ge to enhance the sintering and mechanical properties of a Ti-7Fe based powder metallurgy alloy (Ge = 0, 2, and 4 wt.%). Germanium is an α-stabilising element with good solubility in the Ti matrix and possesses better biocompatibility than the commonly used aluminium α-stabiliser. After sintering, all alloys exhibited dual-phase microstructures (α and β phase), while an intermetallic Ti5Ge3 also formed in Ti-7Fe-4Ge. Despite being an α-stabilising element, germanium primarily segregated to the β phase regions in the Ti-7Fe-xGe alloys. Gradual increments of the sintered density of the alloys were observed with increasing Ge additions. The sintered Ti-7Fe-xGe alloys were solution treated to exploit the metastability of the retained β phase. After solution treatment at 1000 °C, the alloys predominantly exhibited β phase with minor traces of martensitic athermal ω-phase. Germanium suppressed the formation of the athermal ω-phase and reduced the stability of the β phase. The solution-treated Ti-7Fe-2Ge alloy is most promising for implant applications with a relatively low compressive Young's modulus (∼ 70 GPa) and high yield strength (∼ 1450 MPa), which leads to an outstanding elastic admissible strain of ∼ 2.2%.

Correlation between microstructure and mechanical properties of novel Co-Ni-based powder metallurgy superalloy

A novel Co-Ni-based superalloy was manufactured by powder metallurgy (PM) process. The microstructure and mechanical properties of PM alloy were analyzed in detail and compared with the corresponding casting alloy. After cold swaging to 66% and subsequent aging for 800 °C for 3 h on solution treated (ST) PM alloy, the yield strengths of PM superalloy can be doubled and tripled to be 1500 and 2265 MPa respectively, as compared with 700 MPa of ST PM alloy. In contrast, for the same casting alloy after subjected to similar treatments, their corresponding yield strengths were 1100 and 1650 MPa, respectively, which are much lower than these of PM alloy. Strengthening mechanism of both PM and casting alloys were quantitatively calculated, unmasking that the higher mechanical property of PM alloy can be mainly ascribed to the higher contribution from grain boundary and precipitation strengthening.

Microstructure and tensile properties of aluminum powder metallurgy alloy prepared by a novel low-pressure sintering

This paper proposed a novel low-pressure sintering process contraposing to characteristics of pre-alloyed aluminum powders and analyzed its feasibility. The low pressure was set to 0.1 MPa in this study. Meanwhile, 0 MPa and 10 MPa were set as control group. With gas-atomized 2024 aluminum powders as raw material, the microstructure and tensile properties of specimens sintered under three orders of magnitude of pressure (0 MPa, 0.1 MPa and 10 MPa) at two representative temperatures (525 °C and 575 °C) were compared. The results showed that it was difficult for pressureless sintering (0 MPa) to densify pre-alloyed aluminum powders, but low-pressure sintering could. As the liquid phase formed at supersolidus temperature was squeezed out, the loss of alloying elements such as Cu and Mg, which would play an important role in subsequent heat treatment, during low-pressure sintering was apparently less than that of 10 MPa. The density of aluminum sintered under 0.1 MPa at 575 °C was 2.732 g/cm3 and the ultimate tensile strength was 228.16 MPa with ductility of 12 %, which achieved a good balance of plasticity and strength. These findings will bring new insights to the industrialization of aluminum powder metallurgy (APM).

Evolution of the Microstructure and Mechanical Properties of a Ti35Nb2Sn Alloy Post-Processed by Hot Isostatic Pressing for Biomedical Applications

The HIP post-processing step is required for developing next generation of advanced powder metallurgy titanium alloys for orthopedic and dental applications. The influence of the hot isostatic pressing (HIP) post-processing step on structural and phase changes, porosity healing, and mechanical strength in a powder metallurgy Ti35Nb2Sn alloy was studied. Powders were pressed at room temperature at 750 MPa, and then sintered at 1350 °C in a vacuum for 3 h. The standard HIP process at 1200 °C and 150 MPa for 3 h was performed to study its effect on a Ti35Nb2Sn powder metallurgy alloy. The influence of the HIP process and cold rate on the density, microstructure, quantity of interstitial elements, mechanical strength, and Young’s modulus was investigated. HIP post-processing for 2 h at 1200 °C and 150 MPa led to greater porosity reduction and a marked retention of the β phase at room temperature. The slow cooling rate during the HIP process affected phase stability, with a large amount of α”-phase precipitate, which decreased the titanium alloy’s yield strength.

Cost-affordable and qualified powder metallurgy metastable beta titanium alloy by designing short-process consolidation and processing

Short-time processing route has been designed to manufacture cost-affordable and high-quality powder metallurgy (PM) metastable β titanium alloy, containing rapid powder consolidation (modified thermomechanical pressing), one-step thermomechanical processing (simple open die uniaxial hot forging by industrial press) and fast heat treatment (one-step annealing at various temperatures for only one hour). Based on comprehensive microstructure characterizations and mechanical property examinations, underlying microstructural evolution mechanism and microstructure-property relationship of the produced alloys were uncovered and elucidated thoroughly. Homogeneous macrostructure and fine-grain microstructure without undissolved particles and large pores are obtained for the alloy after thermomechanical powder consolidation as a result of the concurrent effect of external deformation and high-temperature diffusion. One-step open-die forging is verified to produce full-dense and sound PM alloy pancake with large-scale and high strength. Attributed to the harmonious concurrence of hierarchical α precipitation and heterogeneous grain structure, synergistic strength-ductility combinations are achieved for the alloy after specific processing and heat treatment with the tensile strength and strain at failure values of 1386.5 MPa/7.3% and 1252.3 MPa/9.0%, respectively. These strength-ductility combinations are comparable and/or even better than other metastable β titanium alloys prepared by some PM and ingot metallurgy approaches with relatively high cost and time consumption.

Iron Carbon Masteralloy as Sintering Activator for Low Alloy Powder Metallurgy Steels

In real industrial environment there is always a difference between ideal theoretical condition and real production condition which bears the risk of producing defective or low quality parts. Getting closer to this ideal situation requires more effort and investment which tends to increase the production cost. In the P/M production lines, the sintering stage is one of the most critical processes. Maintaining an open continuous sintering furnace in an ideal condition is a challenge, and this issue gets more pronounced when using alloy powder containing oxygen-sensitive elements such as Cr or Mn which provide good hardenability at low cost but on the other hand form stable oxides that weaken the sintering contacts if they are not reduced properly. In the present study, using a carbon master alloy as a sintering enhancer in the sintering process of Cr-Mo alloyed powder compacts has been investigated. For clearly depicting the effect of carbon master alloy addition on carbon dissolution and deoxidation, sintering was done in argon as inert atmosphere to avoid other reducing agents such as H2. The physical and mechanical properties of the sintered specimens were investigated, and thermal chemical analysis by DIL/MS and carbon/oxygen measurements were performed. The experiments showed that adding iron-carbon masteralloys promote the sintering processes such as reduction of oxides and carbon dissolution in the early stages of sintering, resulting in better properties after final sintering.

Mechanical and Metallurgical Studies on Thixoextruded Al-Si Alloys

Thixoforming is a commonly known material processing technique that involves the fabrication of materials between solidus and liquidus temperatures. One of the prerequisites for this process is that the microstructure of the feedstock material must contain solid near-globular grains in a liquid matrix and a broad solidus-to-liquidus transition range. The aim of the present work is to study the application of Al-Si powder metallurgy (P/M) alloy in the thixoextrusion process and to evaluate the properties before and after extrusion. Al-Si P/M alloys were prepared for various Si compositions (1-7%) and Mg compositions (0.2-0.8%). The best among the Al-4Si and Al-4Si-0.6 Mg were selected based on hardness and density results. Differential thermal analysis revealed the solidus and liquidus temperatures to be 557 and 642 °C for Al-Si alloy and 564 and 636 °C for Al-4Si-0.6 Mg alloy, respectively. Compaction temperature and holding time studies have been carried out and the corresponding optimized parameters are found to be 550 °C and 60 min. Thixoextrusion was performed on the hot compacted preforms for three temperatures namely 560, 580 and 600 °C, respectively. An extrusion ratio of 4:1, strain rates of 0.1, 0.2 and 0.3 s−1 and die approach angle of 60° were used for the tests. Extrudates were divided into three regions namely front, middle and end parts to analyse its mechanical and metallurgical properties. Micrographic analysis revealed the presence of globular grains in the specimen. Hardness values showed a marginal increase from 45 to 60 HV for Al-4Si alloy and 42-80 HV for Al-4Si-0.6 Mg alloy.

Experimental and numerical investigation on fretting fatigue behavior of Nickel-based single crystal superalloy at high temperature

The fretting fatigue behaviors of a nickel-based single crystal superalloy in contact with a powder metallurgy alloy at 600 °C are investigated. Fretting fatigue tests are conducted by using a novel high temperature fretting fatigue test apparatus that is developed, and the crystal plasticity finite element method is used to analyze the contact stress and activations of slip systems. The results show that the fretting conditions are partial slip regime for all loading conditions, and severe wear damage occurs across the slip region, which is accompanied by surface delamination and micro crack. Fretting fatigue cracks mainly initiate at the contact leading edge area, i.e., the stress concentration zone. The cracks grow along the (100) plane when multiple octahedral slip systems are activated simultaneously, or could be eliminated by wear. Considering the effects of both crystallographic slip and wear on the fretting fatigue damage, an improved fretting fatigue damage parameter, RA , is proposed to predict the fretting fatigue life. The predicted results agree well with the test results. • A novel high temperature fretting fatigue test apparatus has been developed. • Crystal plasticity finite element method is applied to calculate the contact stress and strain. • Fretting fatigue damage mechanism is proposed considering wear and cracking. • A damage parameter, RA , is proposed to describe surface damage and predict fretting fatigue life.

Hot Processing of Powder Metallurgy and Wrought Ti-6Al-4V Alloy with Large Total Deformation: Physical Modeling and Verification by Rolling

The influence of the total deformation amount on the microstructure and selected properties of Ti-6Al-4V alloy was determined in this study. Multi-axis compression tests on the MaxStrain module were performed to obtain large strains. Starting material for the research was obtained by the powder metallurgy (PM) route. Plastically processed cast alloy of the same chemical composition as PM alloy was also tested as reference material. The tests were performed with the cooling of samples between successive deformation stages, which allowed for the simulation of the temperature drop occurring during industrial processes. The multi-stage deformation ability of PM Ti-6Al-4V alloy without decohesion was confirmed. It has also been shown that the application of increasing total strain at a controlled temperature changes the samples resulting in the refinement of the microstructure and leads to the fragmentation of lamellae. The results obtained from MaxStrain tests were verified by multi-stage hot-rolling tests. Defect-free products were obtained, whose good quality was confirmed by the microstructural observations as well as by the investigations of their properties. The results of the rolling tests confirmed the possibility of hot processing of Ti-6Al-4V alloy compacts in industrial conditions, applying large total strain.

A microstructural and mechanical property investigation of a hot upset forged 2xxx series aluminum powder metallurgy alloy reinforced with AlN

Abstract Metal-matrix composites (MMC) of a 2000-series aluminum alloy coupled with AlN were fabricated through a commercially-relevant aluminum powder metallurgy (APM) approach. Cylindrical preforms containing 0–5 vol% AlN were produced to investigate the mechanical properties and microstructure evolution through hot upset forging. Specimen were deformed to a maximum strain of 0.15–1.55 mm/mm at rates of 0.1–1.0 s−1. TEM observations of forged products indicated the Al–AlN interfaces were free of defects and of high quality. Near-full (>99.5% theoretical) densities were observed at 1.40 mm/mm. At this strain, a substantial increase in all tensile properties was observed. An elastic modulus of 77 GPa was realized in a forged product with 5% AlN, accompanied by a 0.2% offset yield strength of 325 MPa and a UTS of at least 400 MPa. Versus an undeformed sample, forged MMC’s exhibited up to a five-fold increase in tensile ductility. Likewise, improvements of up to 98 MPa (57%) in fatigue strength were recorded. Mechanical gains were a result of densification and residual oxide disruption, as well as the enhanced dispersion of the AlN phase.

In-situ tensile deformation behavior of powder metallurgy Ti6Al4V alloys

In this study, in-situ tensile deformation behavior of powder metallurgy (PM) Ti6Al4V alloys was investigated to analyze the crack initiation and propagation. Accordingly, the fracture mechanisms of the as-sintered and forged PM alloys were summarized. At the initial stage of plastic deformation, cracks appeared in the stress concentration area of pores in the as-sintered Ti6Al4V alloy, and the crack propagation direction was along the phase boundary. Due to the existence of pores, early fracture was obtained, resulting in low elongation of 6.3%. After forging, the crack initiation occurred between α lamellar structure, and the propagation direction was along the lamellar direction. The fine lamellar structure in different directions in the forged PM Ti6Al4V alloy can hinder the crack propagation, thus improving the plasticity. As a result, better comprehensive mechanical performance was obtained in the forged sample, with UTS of 960 MPa, YS of 850 MPa, and EL of 16%.

Micro-abrasive Wear Behavior of Nitrided and Multilayer Coated High Vanadium Powder Metallurgy Alloy

The micro-abrasive behavior of plasma nitrided Vanadis 10, a high vanadium powder metallurgy alloy, combined with TiCN/AlTiN/CrAlTiN/CrN multilayer film was evaluated and compared with different treatment conditions. Microstructural evolution with treatments was evaluated. The tribological behavior was accessed using the fixed ball micro-abrasion test and SiC as abrasive. The counter-body was an AISI 52100 steel sphere (O 25.4 mm), the SiC abrasive slurry concentration was 0.50 g/cm3, the rotary speed was set at 75 rpm, and the applied load was 0.49 N. The wear crater was characterized by scanning electron microscopy (SEM). Results indicated that the film is effective in reducing the wear coefficient in more than 80 pct for all conditions compared with Vanadis 10. Nitriding treatments impaired the samples’ wear resistance because of the presence of cracks in this layer. Sliding/grooving abrasion was observed for the conditions with higher wear coefficients. The change in the micro-abrasion wear mechanism from grooving abrasion to rolling abrasion is attributed to the protection of the surface by the hard multilayer coating, producing a reduction in the wear coefficient.

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.

Effect of Mn on microstructure and properties of Cu-12Al powder metallurgy alloy

Cu-12Al-xMn (x = 0, 1, 2, 3, 4%, mass fraction) alloys were produced using powder metallurgy to investigate the effect of Mn content on the alloy’s microstructure and mechanical properties. The Cu-12Al (no Mn) and Cu-12Al-1Mn (1 wt% Mn) alloys consisted of the α + γ phases, where the size of the α grains in the Cu-12Al-1Mn alloy are much larger. Mn effectively inhibited the eutectoid transformation at a concentration above 1 wt%. Furthermore, the β phase was converted to the β′-martensite phase, which had a monoclinic structure after slow cooling. The phases of the alloy changed from the α + γ phases to the α + β′ + γ phases with the further addition of Mn, and the tensile strength of the 3 wt% Mn alloy was 380.59 MPa. The addition of Mn did not have a significant effect on the density of the alloy.