Powder Metallurgical Process Research Articles

Additive Manufacturing of Textured FePrCuB Permanent Magnets.

Permanent magnets based on FePrCuB were realized on a laboratory scale through additive manufacturing (laser powder bed fusion, L-PBF) and book mold casting (reference). A well-adjusted two-stage heat treatment of the as-cast/as-printed FePrCuB alloys produces hard magnetic properties without the need for subsequent powder metallurgical processing. This resulted in a coercivity of 0.67 T, remanence of 0.67 T and maximum energy density of 69.8 kJ/m3 for the printed parts. While the annealed book-mold-cast FePrCuB alloys are easy-plane permanent magnets (BMC magnet), the printed magnets are characterized by a distinct, predominantly directional microstructure that originated from the AM process and was further refined during heat treatment. Due to the higher degree of texturing, the L-PBF magnet has a 26% higher remanence compared to the identically annealed BMC magnet of the same composition.

Effect of boron addition on the microstructure and mechanical properties of refractory Al0.1CrNbVMo high-entropy alloy

The effect of boron (B) addition on the microstructure and mechanical properties of a refractory high-entropy alloy (RHEA) was investigated. The Al0.1CrNbVMo RHEA was doped with 0.015 at.% of B by the powder metallurgical process, and its mechanical properties were compared with undoped RHEA. The microstructures of the undoped and doped RHEAs consisted of a single body-centered cubic matrix phase with homogeneously distributed Al2O3 inclusions. The doped B atoms segregated along grain boundaries and did not form any boride phases. Boron segregation at the grain boundaries was characterized by atom-probe tomography. Compared with the undoped RHEA, the B-doped RHEA showed improved yield strength of 2933 MPa (15% improvement) and ductility of 25.9% (26% improvement). Adding B transformed the fracture surface from intergranular to transgranular due to enhanced grain boundary cohesion induced by B segregation, which resulted in improved ductility. Quantitative analysis was conducted on the undoped and doped alloys to investigate the effect of B on yield strength. The improved yield strength resulting from B doping was attributed to the combined effects of Orowan, dislocation, and B interstitial strengthening. This work demonstrates that B doping of RHEAs is a promising way to overcome their limited room temperature ductility, while maintaining excellent strength.

Sintered Fe-Ni-Si-C alloys

The aim of this research is to explore the effect of nickel content on microstructural development and mechanical properties of sintered Fe-Ni-Si-C alloys. The sintered alloys were prepared from powder mixtures of pre-alloyed Fe-Ni-based powders (nickel contents varied as 0.45, 0.90, 1.80, and 4.00 wt.%) and fixed 4 wt.% silicon carbide powder by using a powder metallurgical process. Sintering was performed in a vacuum furnace at 1250°C for 45 minutes and slow cooling in the furnace. Microstructures of sintered alloys varied with nickel contents. Nickel showed a strong influence on promoting bainitic ferrite/martensite-austenite (BF/M-A) structure formation. Retained austenite in BF/M-A structure was found to increase with increasing nickel content. Tensile properties (strength and elongation value) of sintered alloys increased with increasing nickel content.

Influence of the production route on the phase formation, microstructure and wear behaviour of the high-entropy alloy AlCoCrFeNiTi0.5

Different manufacturing approaches have been investigated regarding their suitability to process high-entropy alloys (HEAs). However, comprehensive investigations on the influence of the production route on the microstructure, phase formation and properties have not been conducted yet. For the current study the alloy AlCoCrFeNiTi0.5 is considered. Previous investigations have proven the formation of phases with predominantly body centred cubic structure for this alloy. Castings are produced by arc-melting. Feedstock material for coating deposition and powder metallurgical processing is produced by inert gas atomisation. For the processing high-velocity-oxygen-fuel (HVOF) thermal spraying and spark plasma sintering (SPS) are applied. Due to the significantly differing process conditions and temperature-time profiles, differences of microstructure, phase formation and resulting properties can be observed. Wear investigations under various conditions have been conducted. Especially under sliding and reciprocating wear conditions the structural defects formed for the thermally sprayed coating cause a reduction of wear resistance. The formation of structural defects could be avoided by SPS. However, the additional tetragonal phase causes a reduction of the wear resistance. The current study contributes to a better understanding of the interaction between process, microstructure and properties.

The study on the characterization of sintered hot forging and austenite stainless steels

The powder metallurgical (PM) process, consisting of compaction and sintering, is commonly used to produce sintered structural parts applied in various industrial fields. Sintered parts always have porosity due to limited materials transport by solid-state diffusion from powder particles to voids between them. Sintered specimens with low porosity show superior mechanical properties. Hot forging is one of processes for enhancing density of sintered parts. This process was applied to sintered austenitic stainless steels ( 303L, 304L, 310L and 316L). The hot-forged specimens showed increased density. This led to remarkable increase of hardness (up to 5 times). Due to the hot working nature of the process, microscopic changes in the hot-forged specimens during the process were examined. It was found that grain size and volume fraction of twins were significantly deceased.

Study of (Ni,Cr) pre-milling for synthesis of CoFe(NiCr)Mn high entropy alloy by mechanical alloying

Abstract Cr-rich oxide is the most frequently formed on Cr-containing high entropy alloys by a powder metallurgical processing route. Therefore, in this study, the pre-milling of (Ni,Cr) elements was introduced into the CoFe(CrNi)Mn model HEAs synthesized by mechanical alloying to alter the formation behavior of Cr-rich oxides. The results suggest that the pre-milling method can promote the formation of a partial FCC solid solution phase with nanostructured Ni–Cr particles, which facilitates the nucleation of nano-Cr oxides and induces the uniform distribution of fine Cr-rich oxides dispersed in the model HEAs. Besides, the formation of Cr-rich oxides and powder agglomeration can be obstructed by the subsequent secondary ball milling.

Electric discharge coating process variation and its wear properties

The present study elaborates and compare about process variation of electrical discharge coating process through powder mixed and powder metallurgy (semi-sintered) electrode that influences mechanical and metallurgical properties of over duplex stainless. Occurrences of surface roughness, poke, splatters and carters are minimal in deposition of pyrolysis carbon while using the powder metallurgical electrode process of deposition than of powder mixed. Coating layer thickness and porosity are greater in powder mixed having a similar decarburising depth that deserves hardness values with an average of 1,001 HV to 1,010 HV across its section. Pyrolysis carbon restricts alloying element deposition that reduced frictional coefficient with greater wear rate compared with the powder metallurgical process. The metallurgical characterisation is performed through a scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), phase identification through X-ray powder diffraction (XRD), optical microscope (OM), mechanical testing through Vickers microhardness, and wear testing by pin-on-disc (POD) tribometer.

Potential of the Recycling of Grinding Sludge by various Powder Metallurgical Processes

The metalworking industry produces a large amount of waste material by machining. In contrast to conventional machining, the waste material generated during a grinding process is not purely metallic, but consists of abrasives, water, lubricants and metal chips. This mixture is called grinding sludge. In terms of ecological and economical aspects, the recycling of these waste materials is very promising. By separating the individual components of the grinding sludge, the recycling potential of the individual components becomes visible. This study focuses on the recycling of the metallic part. For this purpose, various powder metallurgical processes were performed. The produced samples and their properties were then compared with samples made of conventional PM powder.

Fabrication and evaluation of percent porosity and density reduction of aluminium alloy foam

Aluminium alloy foams are manufactured by various methods, which include foaming of molten aluminum alloy by gas injection and powder metallurgical processing. Non-conventional methods such as direct energy deposition, syntactic method of metal foam fabrication have also been developed for the manufacturing of aluminium alloy foams. Aluminium alloy foams are cellular structure which consists of solid metal such as aluminium, steels and iron with micro pores filled with gases such as hydrogen, carbon di oxide, nitrogen, argon etc. In this research work in order to fabricate aluminum alloy 6063 foam, first aluminium alloy 6063 was melted by using stir casting method as it is economical and simple, 2 wt% titanium hydride was added and mixed into the molten aluminium alloy 6063 at temperature 800 ˚C and then the melt was allowed to cool down to room temperature in order to obtain aluminium alloy 6063 foam. The percent porosity and density of the fabricated aluminium alloy foam is determined with the help of Archimedes principle.

Finite element simulation of sintering of metal-bonded grinding wheels

The grinding wheel properties porosity, particle distribution and the grain holding force influence the surface roughness of the machined workpiece and the performance of the grinding process. These properties of a grinding wheel are in turn defined during tool production. However, the adaptation of the properties of a grinding wheel to the specific grinding task is currently based on empirical knowledge and experience. Understanding the interdependencies from the initial manufacturing to the final grinding results is the key to achieve the target-oriented generation of the grinding wheel properties for the grinding task at hand. With regard to the large number of powder particles for the manufacturing of metal-bonded grinding wheels, an analytical investigation of the powder metallurgical processes is not suitable. Numerical simulations offer a cost and time saving alternative to provide information on the sintering behavior and gain knowledge on the acting mechanism. In this article the sintering of a metal-bonded diamond grinding wheel is modelled and the obtained results are connected to material properties of the resulting grinding layer.

Fabrication of high pours Ti-6A1-4Fe alloy for biomedical application (Dept.M)

In the present study, Ti-6A1-4fe alloy was developed as a cost effective option to replace the traditional Ti-6Al4V alloy in the manufacture of surgical implants because of its larger biocompatibility (free vanadium). This alloy was prepared using the ball milling technique. Novel Ti 6Al-4fe alloy foams with porosity of approximately 70% were fabricated by a space-holder and powder metallurgical process. Irregular NaCl powders with particle size ranging from 100 to 600 um were used as a space holder material. The NaCl in the green compact was removed in hot distilled water at 70°C for times ranging from 1 to 5 h. The sintering process was performed in a vacuum furnace at 1250°C for 2 h. The T1-6A1-4Fe alloy foams displayed an interconnected porous structure resembling bone. The compressive stress and the Young's modulus of the Ti-6A1-4Fe foam were 38±514± GPa and 10.42 GPa, respectively. Both the porous structure and the mechanical properties of the Ti-6Al-4Fe foam were very close to those of natural bone.

PEO Coated Porous Mg/HAp Implant Materials Impregnated with Bioactive Components

In this research the results of the formation of composite materials based on magnesium for the needs of implant surgery are discussed. The synthesis of porous magnesium with the inclusion of hydroxyapatite particles was preformed by means of a powder metallurgical mechanochemical process. The resulting samples were impregnated with bioactive additives such as shilajit. To protect against premature corrosion, the samples were coated with plasma electrolytic oxidation (PEO).

A Novel Non-Equiatomic (W35Ta35Mo15Nb15)95Ni5 Refractory High Entropy Alloy with High Density Fabricated by Powder Metallurgical Process

A non-equiatomic refractory high entropy alloy (RHEA), (W35Ta35Mo15Nb15)95Ni5 with high density of 14.55 g/cm3 was fabricated by powder metallurgical process of mechanical alloying (MA) and spark plasma sintering (SPS). The mechanical alloying behavior of the metallic powders was studied systematically, and the microstructure and phase composition for both the powders and alloys were analyzed. Results show that the crystal consists of the primary solid solution and marginal oxide inclusion (Nb5.7Ni4Ta2.3O2). In addition, the maximum strength, yield strength and fracture strain are, 2562 MPa, 2128 MPa, 8.16%, respectively.

Powder Metallurgical Processing of MMC Pressure Springs Based on Zirconia and TRIP Steel

A novel powder metallurgical fabrication technology for the development of springs based on metastable austenitic steel and magnesia partially stabilized zirconia is introduced. The developed gel casting technique uses the gelation of alginates in contact with bivalent ions and allows the variation of fabrication parameter such as composition of the starting slurry, wire thickness, coil number, and distance between the single coils. The starting slurry contains 16‐7‐3 (Cr–Mn–Ni) steel and zirconia powders as well as sodium alginate and is subsequently injected into a hardener solution to form rubbery strands that are subsequently coiled around a mandrel to form a spring element. Afterward a two‐stage thermal process is performed. The sintered spring elements are characterized by a homogeneous microstructure, and the formation of manganese silicate is registered. In comparison to commercially available coil springs, the developed spring elements show similar deformation behavior up to a deformation of 50%. The composition which contains 10 vol% zirconia and 90 vol% steel particles shows an improved energy absorption capability with 0.19 kJ kg−1 compared with commercially available springs with 0.11 kJ kg−1, and therefore offers the potential for further investigations in the planned application in the area of crash absorbing structures.

Effects of nonmagnetic overlay metals on coercivity of Sm2Fe17N3 magnet powders

The coercivity of Sm2Fe17N3 as a sintered magnet has remained at several % of its huge anisotropy field to date. Control of grain boundary properties has proven to be effective for improving coercivity of modern permanent magnets, and in powder metallurgical processes, overlaying the raw powder surface with a different material can be a powerful methodology for the grain boundary control. Recently, we established a versatile technique for coating powders with minimal surface oxides. In this study, we coated Sm2Fe17N3 powders with 20 nonmagnetic metals by using the technique, and investigated the effects of coating and heat treatment on the coercivity. A simple non-sintering heat treatment was applied to the coated powders to clarify the pure effects of coating excluding intergrain coupling issues. The whole process from powder preparation to coating and heat treatment was undertaken in gloveboxes with a low-oxygen atmosphere. Powder coating was performed by a DC magnetron sputtering method. The powder was continuously stirred during deposition to ensure uniform coating. The magnetic properties of the powders were measured as bonded magnets by using a vibrating sample magnetometer. It was found that a sputter-coating as thick as several nm increased coercivity with most coating elements in varying degrees. However, subsequent heat treatment at 500 °C caused further coercivity changes which depended strongly on the element. The mechanism of the former effect is supposed to be a universal one, whereas the latter seems to be related directly to the chemical details of each element.

Superior mechanical properties and strengthening mechanisms of lightweight AlxCrNbVMo refractory high-entropy alloys (x = 0, 0.5, 1.0) fabricated by the powder metallurgy process

Light and strong AlxCrNbVMo (x = 0, 0.5, and 1.0) refractory high-entropy alloys (RHEAs) were designed and fabricated via a the powder metallurgical process. The microstructure of the AlxCrNbVMo alloys consisted of a single BCC crystalline structure with a sub-micron grain size of 2−3 μm, and small amounts (< 4 vol.%) of fine oxide dispersoids. This homogeneous microstructure, without chemical segregation or micropores was achieved via high-energy ball milling and spark-plasma sintering. The alloys exhibited superior mechanical properties at 25 and 1000℃ compared to those of other RHEAs. Here, CrNbVMo alloy showed a yield strength of 2743 MPa at room temperature. Surprisingly, the yield strength of the CrNbVMo alloy at 1000℃ was 1513 MPa. The specific yield strength of the CrNbVMo alloy was increased by 27 % and 87 % at 25 and 1000℃, respectively, compared to the AlMo0.5NbTa0.5TiZr RHEA, which exhibited so far the highest specific yield strength among the cast RHEAs. The addition of Al to CrNbVMo alloy was advantageous in reducing its reduce density to below 8.0 g/cm3, while the elastic modulus decreased due to the much lower elastic modulus of Al compared to that of the CrNbVMo alloy. Quantitative analysis of the strengthening contributions, showed that the solid solution strengthening, arising from a large misfit effect due to the size and modulus, and the high shear modulus of matrix, was revealed to predominant strengthening mechanism, accounting for over 50 % of the yield strength of the AlxCrNbVMo RHEAs.

Effect of plain strain deformation on grain strengthening mechanism of Fe-Al2O3 metal matrix nanocomposites

The present paper reports the effect of plain strain deformation on grain strengthening mechanism of iron (Fe) - alumina (Al2O3) Metal Matrix Nanocomposites (MMNCs) fabricated through powder metallurgical (P/M) processing. Specimens for the present study were weighed in required amount, ball milled, compacted at a load of 5, 6 and 7 tons followed by sintering in an atmospheric controlled furnace at 1100 °C for 1 hour. Plain strain deformation of samples was carried out at a load of 5 tons under different interfacial condition i.e. dry, solid lubricant and liquid lubricant. XRD studies reveal the formation of iron, alumina and nano iron-aluminate (FeAl2O4) phases respectively. Maximum average sintered density investigated for the specimen is found to be 4.6179 gm/cc compacted under 7 tons of load and minimum sintered density is found to be 4.4572 gm/cc for specimen compacted under 5 tons of load. Overall, fabricated Fe-Al2O3 metal matrix nanocomposites with powder metallurgy route when characterized for plain strain deformation shows strengthening between grain and grain boundary which can be a good candidate material for application in railways especially while designing railway structures and tracks.

Effect of recovery and recrystallization on microstructure and magnetic properties of Fe-0.4P rolled sheets

Powder metallurgical processing of the soft magnetic Fe-P alloys is well known. In recent times, the wrought metallurgical processing of these alloys is gaining importance due to the possibility of achieving a good combination of soft magnetic properties by optimising the microstructure through carefully designed heat treatment. The Fe-P alloys are mainly focussed towards realizing an alternative and cost effective alloy to conventional electrical steels. Since not much work on bulk Fe-P alloy system has been reported, we have put efforts on processing Fe-P alloy by wrought metallurgy route to bring out comprehensively the dependence of the microstructure on magnetic properties. Fe-0.4 wt.% P alloy sheets (~0.5 mm) were prepared by adopting the conventional melting, forging and rolling, and heat treated at various temperatures (500 – 1000 °C). Recovery and recrystallization behaviour was investigated using electron back scattered diffraction technique and correlated with the microstructural parameters and mechanical/magnetic properties. Transmission electron microscopy studies revealed the formation of Fe3P nanoprecipitates (2-4 nm) leading to a reduction in lattice strain as confirmed from X-Ray diffraction data analysis. Heat treatment at 1000 °C/1h resulted in the formation of fully recrystallized coarse grain structure with coercivity of 80 A/m. Upon further aging at 300 - 500 °C/0.5 h, the coercivity reduced to 43 A/m with a core loss of 347 W/kg. The attractive combination of soft magnetic properties was attributed to the coarse grain and nanoprecipitate microstructure with reduction in lattice strain. The results were also compared with commercial non-oriented Si-steels (M700-50A and M400-50A).

Spark Plasma Sintering of Titanium Aluminides: A Progress Review on Processing, Structure-Property Relations, Alloy Development and Challenges

Titanium aluminides (TiAl) have the potential of substituting nickel-based superalloys (NBSAs) in the aerospace industries owing to their lightweight, good mechanical and oxidation properties. Functional simplicity, control of sintering parameters, exceptional sintering speeds, high reproducibility, consistency and safety are the main benefits of spark plasma sintering (SPS) over conventional methods. Though TiAl exhibit excellent high temperature properties, SPS has been employed to improve on the poor ductility at room temperature. Powder metallurgical processing techniques used to promote the formation of refined, homogeneous and contaminant-free structures, favouring improvements in ductility and other properties are discussed. This article further reviews published work on phase constituents, microstructures, alloy developments and mechanical properties of TiAl alloys produced by SPS. Finally, an overview of challenges in as far as the implementation of TiAl in industries of interest are highlighted.

Microstructures and enhanced mechanical properties of an oxide dispersion-strengthened Ni-rich high entropy superalloy fabricated by a powder metallurgical process

Abstract A Ni46Co22Al12Cr8Fe8Ti3Mo1 high entropy superalloy (Ni46 HESA) was fabricated by a powder metallurgical (PM) process. The composition of the alloy was determined through consideration of its PM processability. The alloy had a density of 7.82 g cm−3, which is lower than that of conventional Ni-base superalloys. The microstructure of the bulk alloy consisted of a face-centered cubic γ matrix and an L12 γ′ precipitate with minor amounts of Al2O3 and TiC inclusions. To leverage the advantages of PM processing, yttria (Y2O3) was added and dispersed in the HESA by mechanical alloying, which enhanced its mechanical properties via oxide dispersion strengthening. The oxide dispersion-strengthened Ni46 HESA containing 1 vol% of Y2O3 had a tensile yield strength of 1155 MPa at room temperature, 880 MPa at 700 °C, and 485 MPa at 800 °C. The excellent mechanical properties at room and elevated temperatures are attributed to solid solution strengthening, precipitation strengthening, dispersion strengthening, and grain boundary strengthening. The contribution of each strengthening mechanism was analyzed quantitatively using experimentally determined microstructural parameters.