Powder Metallurgy Parts Research Articles

Influence of Cutting Parameters During Machining of Sintered Iron-Copper Parts After Impregnation with Copper-Based Material

Products made from powder materials differ in their structure significantly from parts made using traditional manufacturing methods such as rolling, casting, or forging. Particular interest is in parts made by powder metallurgy (PM) based on iron infiltrated with copper (Fe--C -Cu PM). In the first part of this research, analysis of the Fe--C -Cu PM part is performed. Another aspect of this research is an investigation of the post-processing of PM parts, especially using conventional machining such as turning. Accordingly, the second part of this research is directed at studies of technological assurance of Fe--C -Cu PM part in turning. Different structure of PM parts also requires a different approach to their machining which was the main object of this research. In the evaluation of technological assurance, the surface roughness parameters were chosen as the main quality identifying parameters.

Supersolidus liquid phase sintering of water-atomized low-alloy steel in binder jetting additive manufacturing

This work investigates the feasibility of net shape manufacturing of parts using water-atomized (WA) low-alloy steel with comparable densities to conventional powder metallurgy parts via binder jetting additive manufacturing (BJAM) and supersolidus liquid phase sintering (SLPS). In this study, a modified water-atomized powder grade with similar composition as MPIF FL-4405 was printed and pressure-less sintered under a 95% N2–5% H2 atmosphere. Combinations of two different sintering schedules (direct-sintering and step-sintering) and three different heating rates (1, 3, and 5 °C/min) were applied to study the densification, shrinkage, and microstructural evolution of BJAM parts. This study demonstrated that, although the green density of the BJAM samples was ∼42% of the theoretical density, the sintered parts experienced large linear shrinkage up to ∼25% and reached ∼97% density without compromising shape fidelity. This was ascribed to a more homogeneous pore distribution throughout the part before ramping up to the SLPS region. The synergistic effects of carbon residue, the slow heating rate, and the additional isothermal holding stage at the solid-phase sintering region were determined to be the key factors for sintering BJAM WA low-alloy steel powders with resulting minimal entrapped porosity and good shape fidelity.

Powder Metallurgy Part Manufacturing Concentrated in North-Central Pennsylvania

Powder Metallurgy Part Manufacturing Concentrated in North-Central Pennsylvania

(Digital Presentation) On the Effect of Sizing on Electrochemical Response and Localized Corrosion Behavior of Alumix 123 P/M Alloy

Powder metallurgy (PM) as an additive technique for fabricating parts has been used by many industries such as automotive, aerospace, and medical. However, it has been centered mostly around automotive industry which has benefited from large volume production, low cost, and near-net-shape manufacturing that comes with PM. High demand for producing fuel-efficient and light vehicles in automotive industry provides a driving force for extensive research activity on PM of aluminum alloys. Among different aluminum alloys, PM of 2xxx series are among the best choices due to their good sinterability and mechanical response. But industrial PM parts need post processing treatments such as sizing to meet the real-world applications. While sizing is widely used in industry to provide tighter tolerance, it can also help improving density, fatigue behavior, yield strength, and hardness. But there were very few studies on the effect of sizing on electrochemical response. In this study we produced Alumix 123 PM alloy using a press-and-sinter process and then sizing was applied on some of the samples to compare their long-term electrochemical behavior. The changes in the surface profile and roughness of the samples were investigated using confocal laser scanning microscopy. Electrochemical impedance spectroscopy (EIS) as a powerful technique for investigating long-term electrochemical behavior has been used to find the effect of sizing on corrosion response of Alumix 123 PM. In addition, effect of sizing on localized corrosion and pitting tendency was thoroughly discussed using electrochemical polarization results, scanning electron microscope images, and EIS outcomes.

Laser shock dynamic compaction of aluminum powder

Dynamic compaction establishes shock waves that produces a violent dynamic mechanical response in powder. This process can realize the high-density compaction of powder to fabricate the compact of powder metallurgy parts with excellent performance. A new method for dynamic compaction of powder using laser shock on a small scale is proposed. It exhibits the unique advantages of a pulsed laser, such as high strain rate and dynamic shock force, and suitable for micro-part manufacturing. The experiment on the dynamic compaction of spherical aluminum powder was completed under five different laser energies. The effects of laser energy and powder packing state on the mechanical properties of the final compact and Microstructure of the compact, including the upper, failure, and cross section surfaces, were analyzed. Results showed that the mechanical properties of the aluminum compacts gradually improved with the increase of laser energy. The nearly fully dense aluminum compacts were successfully compressed at 1800 mJ laser energy with a final relative density of 99.72%. Moreover, the Microhardness of the compacts improved by approximately 60%. The simulation results using multi-particle finite element method (MPFEM) show that with the propagation of the generated shock wave in the compact, particles had large plastic deformation that filled the pores during the laser shock dynamic compaction of aluminum powder. The simulation and experimental results show that the main connection mechanism of particles is cold welding. The dense packing of powder before compaction could considerably improve the propagation of shock waves, and the initiation and growth of inter-particle cracks were reduced.

EXPERIMENTAL INVESTIGATION OF WELD JOINTS BETWEEN SINTERED NB MODIFIED HK30 STAINLESS STEEL AND WROUGHT/CAST STAINLESS STEELS

Very important property of powder metallurgy parts is ability to join to components produced by different manufacturing technologies or dissimilar materials. Properties of powder metallurgy Nb modified HK30 components are highly influenced by conditions applied during sintering. Weldability of sintered components can be improved using favorable sintering conditions. In this regard, effect of sintering parameters on fusion weldability of Nb modified HK30 is presented in this paper. Investigation of weld joints between HK30, produced by different sintering conditions, and cast HK30 stainless steel is performed. In addition, examination of welds between sintered HK30 and wrought 304 stainless steel is also performed. Microstructural examination and hardness testing of fusion zones and heat affected zones were done for different combinations of base material.

Detection of cracks in green products of powder metallurgy by means of laser vibrometry

Cracking of green parts in powder metallurgy (PM) is a big concern in PM industry. Detection of cracks in green parts before sintering can prevent recycling of already sintered parts or production of defective ones. As opposed to sintered parts, where the presence of cracks is well revealed by impact spectroscopy, it is challenging for green parts. The reason is an extremely low mechanical quality factor of these parts composed of compacted but non-sintered metal powder particles. Low mechanical integrity of particles causes the absence of pronounced resonances of the parts. The aim of the study was to test a possibility to discerning healthy and cracked green parts using spectral characteristics of signals obtained by laser vibromery. Four similar green PM gear wheels made of steel powder were obtained from a PM manufacturing company, two of them were healthy and two with simulated cracks that appeared in the area of stress concentration between the hub and the disc. The experimental setup included a Polytec PSV-500 scanning laser vibrometer and a Bruel&Kjer vibration stand type 4824. Integrated spectrograms in the frequency range 50 – 3500 Hz were recorded upon a 95-point network on the gear surface at different vibration intensities proportionally graded in the range from 1 to 5. Comparison of the 3D (frequency-intensity-amplitude) vibration spectrograms showed that the defected specimens with cracks differed from the healthy ones in the following features: resonance frequency shift and/or splitting of resonances when the load changes. The study confirmed the principal possibility of cracks detection in green PM parts using laser vibrometry regardless the crack location in the part. The aim of further studies is to determine the sensitivity limit in terms of crack size.

A review on high velocity compaction mechanism of powder metallurgy.

High Velocity Compaction (HVC) is a key technology to realize the performance of powder metallurgy parts "three high and one low" (high density, high precision, high performance, and low cost). The main purpose of this paper is to summarize the research results at home and abroad on the forming mechanism, forming influencing factors and theoretical basis of high velocity compaction. This paper analyzes and summarizes the literature and monographs at home and abroad through literature research methods to obtain the research results of high velocity powder metallurgy compaction, so as to fully and correctly understand the research progress, development trends and application prospects of high velocity compaction. This paper expounds the technical characteristics, advantages and limitations of high velocity compaction, and analyzes and looks forward to its development trend, application prospect and expansion field, So as to provide reference and reference for the future research and application direction of high velocity compaction technology.

Nanostructured strain-hardened aluminum-magnesium alloys modified by C60 fullerene obtained by powder metallurgy Part 2. The effect of magnesium concentration on physical and mechanical properties

This paper is intended to continue the studies of magnesium effects on the structural phase composition, physical and mechanical properties of the nanostructured strain-hardened aluminum-magnesium alloys modified with C60 fullerene [1]. Previously obtained mechanically alloyed composite powders [1] were consolidated by direct hot extrusion method. Consolidation parameters were chosen based on previous studies of the structure and phase composition formation during mechanical alloying and heat treatment. It was found that an increase in magnesium concentration improves mechanical properties of extruded nanosructured composite materials, and additives modified by C60 fullerene stabilize the grain structure and slow down decomposition of α solid solution of magnesium in aluminum to 300 °C. Under similar thermobaric treatment Al82Mg18 (AMg18) not modified with C60 demonstrates a reduced α solid solution lattice constant and an increased average crystallite size. These processes are accompanied by sequential formation of γ, β′, and β phases, while γ and β′ are intermediate phases. The grain structure of extruded samples is typical for materials obtained in this way – grains are closely packed, elongated and oriented along the extrusion axis. The grain structure of extruded samples inherits the morphology of mechanically alloyed powders. Thus, mechanical alloying methods followed by intense plastic deformation (extrusion) improved mechanical properties significantly. Materials with ultimate tensile strength of 880 MPa; ultimate bending strength of 1100 MPa; microhardness up to 3300 MPa; and with the same density of 2.4–2.6 g/cm3 were obtained. This result demonstrates the prospects for using powder metallurgy techniques in the production of new nanostructured composite materials modified by C60 fullerene with improved physical and mechanical properties.

Experimental analysis and parametric optimization of drilling process for ferrous clay composite using GRA-PCA approach

The use of materials mixture with non-metallic ingredients composed by powder metallurgy (PM) are getting increased attention in many industries. The newly developed composite material is mainly applied to the structural parts in the many industries. PM parts machining is still a challenge and known as difficult-to-cut metals for manufacturers because of the many factors mainly porosity, Nano particles and complex microstructure. In this work, the mechanical properties like density and porosity along with the machinability in drilling of a newly developed sintered powder metallurgy (P/M) components having Nano-particles of bentonite clay as machinability enhancer is evaluated by a standard twist drill. The impact of this paper aims to reveal the key cutting phenomena i.e. generation of thrust forces, quality of surface roughness, and new insight into the machining mechanism of sintered material. The parameters involved in the machinability study are as speed, feed rate and Nano-particles of bentonite clay for controlling the parametric variables on the response parameters. The speed has the major (95%) effect on the thrust force where the clay percentage has the major (84%) effect on the surface roughness. The less thrust force and low surface roughness have been achieved at 5% clay with 910 rpm and 1% clay with 2265 rpm, respectively. Further, the hybrid grey relational analysis along with principal component analysis (GRA-PCA) has been carried out to find the optimum condition. The less thrust force (Ft) and low surface roughness (Ra) has been found at 1% clay and 910 rpm. The confirmation of optimal process parameters has been made with overall evaluation criteria (OEC) and found the same optimum condition. The X-ray diffraction despises homogeneous mixture of clay in ferrous clay composite. The SEM analysis exposed the presence of clay particles and plastically deformed area during drilling of ferrous clay composite. Thus, this analysis show that the 1% of Nano-particles of bentonite clay is helpful as porosity fillers or machinability enhancer at low speed and within acceptable mechanical properties.

Laser Powder Bed Fusion with Intentionally-Seeded Porosity for Prototyping of Powder Metallurgy Parts

Laser powder bed fusion (LPBF) additive manufacturing technology was used to produce functional prototypes of powder metallurgy (PM) components from high carbon content, iron-based water-atomized powders. The melt pool modeling and design of experiment approaches were combined in order to determine the LPBF operation window allowing to print parts with components similar to the PM in terms of density, microstructure and mechanical properties. The size, morphology and distribution of processing-induced pores were evaluated using computed tomography, while a microstructure analysis was carried out using X-ray diffraction and scanning electron microscopy, and the mechanical properties were evaluated using tensile and unnotched Charpy testing. It was demonstrated that LPBF technology could effectively be used for the just-in-time manufacture of high-fidelity functional prototypes of PM parts from iron-based powders.

Sinter Hardening of Cr-Mo Pre-Alloyed Steels as a Function of the Carbon Content

Abstract Sinter hardening is a technique that is frequently employed in powder metallurgy parts production since it is an economical, clean, and environmentally friendly procedure. Since the cooling rates are however significantly lower than e.g. in water or oil quenching, alloy systems have to be used that ensure martensite formation already at moderate cooling rates. In the present study, quenching dilatometry was used to investigate the hardenability of two types of Cr pre-alloyed steels, Fe-3Cr-0.5Mo and Fe-1.5Cr-0.2Mo, the carbon content being varied, and sinter hardening diagrams were plotted. It showed that this parameter has a pronounced influence on the hardenability of the 3 % Cr alloy; in particular in the range 0.3…0.4 % combined C. For the lower alloyed system, in contrast, even 0.52 % combined C was insufficient to ensure martensite formation at the cooling rates typical for industrial sinter hardening. Finally, impact test specimens were prepared by sinter hardening at cooling rates typical for industry, and hardness, as well as impact energy, were determined.

Mechanical Properties and Corrosion Resistance of Borosintered Distaloy Steels

Distaloy SA is a sponge iron powder (nominal composition: Fe-1.75Ni-1.5Cu-0.5Mo) widely used in the production of powder metallurgy (P/M) parts in the automotive industry. In this study, Distaloy SA powders were sintered in two different atmospheres, one consisting of pure Ar gas (traditional sintering) and the other consisting of a mixture of 90 wt.% B4C and 10 wt.% NaBF4 powders (borosintering). To investigate the effects of the different sintering atmospheres, the P/M samples were characterized using density measurements, surface roughness tests, scanning electron microscopy, energy dispersive x-ray spectroscopy, x-ray diffraction, microhardness measurements, nanoindentation experiments, wear tests and corrosion tests. On the surface of the borosintered samples, a 160-325 µm thick double-phase FeB + Fe2B boride layer was formed. The hardness (1405-1688 HV) and elastic modulus (122.21-162.42 GPa) of the surface were significantly improved with the borosintering treatment compared to conventional sintering (215-250 HV, 63.28-94.86 GPa). Borosintering also provided low friction coefficient values and an increased wear resistance compared to conventional sintering. A significant increase in corrosion resistance was also observed with the borosintering treatment in three different solutions. The corrosion rates of both sintered and borosintered samples were ranked as NaCl < HCl < H2SO4. The borosintered samples displayed superior corrosion resistance compared to the sintered samples, especially in the acid solutions. The results of this study show that significant cost savings can be achieved by combining the boriding and sintering treatments in a single borosintering process.

Wear Resistance of Nano Surface Modified Layer Based on Powder Metallurgy Parts in Stone Carving Design

Wear Resistance of Nano Surface Modified Layer Based on Powder Metallurgy Parts in Stone Carving Design

Effect of fine powder particles on quality of binder jetting parts

Abstract Despite their desired effects on quality metrics of powder metallurgy parts, fine powder materials are rarely used in powder-based additive manufacturing as powder feedstock materials due to their poor flowability and inefficient layer recoating. As such, process-structure-property relationships of powder-based AM processes have been explored primarily for coarse powder particle sizes (i.e., 25 μm–150 μm in diameter). With the new developments in powder recoating systems in modern binder jetting additive manufacturing (BJ-AM) printers, it seems now feasible to process fine powder materials that have average particle size of ∼10 μm (or smaller). In the current research, the use of fine copper powders (average particle size of 5 μm) in BJ process and its effects on green and final part properties are experimentally investigated. Specially, the authors studied the effects of different powder recoating settings on the density of printed green parts. The density of the sintered parts was also explored for various sintering parameters (i.e., heating rate and peak sintering temperature). Linear/volumetric shrinkage, microstructure and mechanical characteristics of sintered specimens were explored, and the results were compared to those of copper specimens made via coarse powder materials. The results indicated that fine copper powder resulted in parts with properties (UTS of 179.4 MPa and elongation of 42.2 %) greater than bimodal powder parts, which in turn eliminates extra time and work needed for powder mixing ratio optimization and blending process.

Effect of hot isostatic pressing on densification, microstructure and nanoindentation behaviour of Mg\u2013SiC nanocomposites

The production of fully dense nanocomposites with a homogeneous distribution of nanoparticles through powder metallurgy (PM) techniques is challenging. Additionally to mechanical milling, pressing and sintering, a final consolidation process is needed to fully densify the nanocomposite. Hot isostatic pressing (HIP) is a promising alternative method to other hot forming processes to eliminate porosity in these PM parts. In contrast to hot extrusion, for instance, isotropic properties are achieved, and textures, as they are usually observed in Mg after uniaxial deformation, are avoided. Here, we evaluate the effect of HIP on the densification, microstructure and (nano)hardness of Mg–SiC nanocomposites. Even though density increased indeed, we observed no increase in the mechanical properties, due to significant heterogeneity in the microstructure. SiC-free regions with a higher grain size developed. Local nanohardness measurements of the HIPed Mg nanocomposite revealed that these regions had a significantly lower nanohardness than the SiC-containing regions. Under consideration of mechanisms reported to be active in Mg in the pressure and temperature regime we used, we conclude that grain growth is the most likely mechanism leading to the microstructure observed after HIP. This is driven by the thermodynamic pressure to decrease the grain boundary energy and facilitated by a slightly inhomogeneous distribution of SiC nanoparticles in the sintered nanocomposite.

First demonstration of photoelectrochemical water splitting by commercial W–Cu powder metallurgy parts converted to highly porous 3D WO3/W skeletons

Hydrogen evolution through photoelectrochemical (PEC) water splitting by tungsten oxide-based photoanodes, as a stable and environmental-friendly material with moderate band gap, has attracted significant interest in recent years. The performance of WO3 photoanode could be hindered by its poor oxygen evolution reaction kinetics and high charge carrier recombination rate. Additionally, scalable and cost-effective commercial procedure to prepare nanostructured electrodes is still challenging. We present, for the first time, a novel and scalable method to fabricate highly efficient self-supported WO3/W nanostructured photoanodes from commercial W–Cu powder metallurgy (P/M) parts for water splitting. The electrodes were prepared by electrochemical etching of Cu networks followed by hydrothermal growth of WO3 nanoflakes. Interconnected channels of W skeleton provided high active surface area for the growth of WO3 nanoflakes with a thickness of ~40 nm and lateral dimension of ~250 nm. The optimized photoelectrode having 35% interconnected porosity exhibited an impressive current density of 4.36 mA cm−2 comprising a remarkable photocurrent of 1.71 mA cm−2 at 1.23 V vs. RHE under 100 mW cm−2 simulated sunlight. This achievement is amongst the highest reported photocurrents for WO3 photoelectrodes with tungsten substrate reported so far. Impedance and Mott-Schottky analyses evidenced fast charge transfer, low recombination rate, and accelerated O2 detachment provided by optimum 3D porous WO3/W electrode. Due to the nature of the commercial P/M parts and low-temperature hydrothermal processing, the procedure is cost-effective and scalable which can pave a new route for the fabrication of highly porous and efficient water splitting electrodes.

Material Removal Mechanism of Green Machining on Powder Metallurgy Parts during Orthogonal Cutting

Due to its energy‐saving and cost‐reducing characteristics, a novel green machining technique for powder metallurgy (PM) parts is attracting increasing concern. Unlike in the traditional PM machining technique, in the PM green‐machining method arranges, the processing operation is performed before sintering. Since the pristine PM compacts are relatively soft because it just bonds the particles together, direct cutting on pristine PM compacts is a tool‐saving and cost‐effective manufacturing technique and its cutting mechanism is different from that of both solid plastic metals and conventional brittle materials because of the special characteristics of a discontinuous material. The influences of cutting parameters on machined surface roughness are investigated by orthogonal cutting experiments. The results show that the machined surface roughness decreases with increasing cutting thickness and rounded cutting edge radius and slightly increases with increasing rake angle. It is suggested that these results are contrary to the long‐held notions of machined surface roughness. Moreover, a geometric model illustrating the PM green‐machining process was established to reveal the mechanism of material removal and machined surface formation. This model shows that the material removal of PM is composed of particle shearing deformation, peeling, and ploughing/extruding. Finally, this machining model was validated through observations of machined surface morphology and chip morphology.

Artificial Auditory Perception Pattern Recognition System Based on Spatiotemporal Convolutional Neural Network

It is difficult to combine human sensory cognition with quality detection to form a pattern recognition system based on human perception. In the future, miniature stepper motor modules will be widely used in advanced intelligent equipment. However, the reducer module based on powder metallurgy parts and the stepper motor may have various defects during operation, with varying definitions of those that affect the user comfort. It is tremendously important to develop an intelligent system to effectively simulate human senses. In this work, an elaborated personification of the perceptual system is proposed to simulate the ventral and flow of the human perception system: two branch systems consisting of a spatiotemporal convolutional neural network (S-CNN) and a concatenated HoppingNet temporal convolutional neural network (T-CNN). To ensure high robustness of the system, we combined principal component analysis (PCA) with the opinions of an experienced quality control (QC) team members to screen the data, and used a bionic ear to simulate human perception characteristics. After repeated comparisons of the tester, the results show that our anthropoid pattern sensing system has high accuracy and robustness for a stepper motor module.

Densification of complex shape ceramics parts by SPS

Spark Plasma Sintering (SPS) equipments, with higher productivity and hybrid heating modes, allow reducing thermal gradients in large samples and broaden their application potential. Furthermore, strong shape limitations remain: only simple shapes can be obtained because of the use of uniaxial pressure.The aim of this paper is to propose a SPS densification method for complex shape ceramic or powder metallurgy parts, without any modification of the tools and equipment. The samples to be sintered are placed in a powder bed in the classical die used in SPS. Different powder beds have been tested.A numerical model was developed in order to allow a rapid simulation of the force field around a part surrounded by a powder bed in a SPS tool. The optimization of the operating conditions was carried out, first, on small simple-shape samples, then, on complex geometry parts which were densified to demonstrate the feasibility of the proposed sintering process.