Powder Metallurgy Materials Research Articles

Shear band formation and wear mechanisms of Ti-6Al-4V powder metallurgy materials with different densities

Ti-6Al-4V powder metallurgy materials with different densities were prepared by hot isostatic pressing technology. Shear band formation and wear mechanisms of the powder metallurgy materials were studied. The wear mechanisms of the powder metallurgy material were revealed that the micro-void torn and accumulated built-up edge in sticking friction and sticking zones, respectively. The wear mechanism of tool rake face was varied when the material density deceased. The shear plane shifted to the residual micro-void, which made a difference on fluctuation of cutting force and caused the appearance of severe micro-fluctuation. The micro-fluctuation of cutting force was weakened with decreasing the material density. Therefore, occasional random shear model of the powder metallurgy material was verified, and the progressions of chip morphology characteristic parameters with material density were studied, the micro-void on improved shear stress concentration. It could be concluded that the shear band mechanism of serrated chip in machining of titanium alloy was a catastrophic shear.

A study on friction and wear reduction due to porosity in powder metallurgic gear materials

It has been widely acknowledged that controlled texturing on a surface can contribute to friction and wear reduction at lubricated sliding contact interfaces. This paper investigates the influence on friction and wear of different pore size distributions of powder metallurgy gear materials. The pore sizes are controlled by different densities of the powder metallurgic materials. Two different kinds of powder metallurgy (PM) gear materials were applied and a standard gear material are used as a reference. The friction and wear coefficients of PM materials sliding on PM materials increase with increasing pore size. The friction and wear coefficients of regular steel sliding on PM materials decrease with increasing pore size. No matter what the material of the disc, peeling is one of the main damage mechanisms of powder metallurgy pins with the biggest porosity.

Effects of diffusion alloying on the microstructure and properties of TiC-reinforced Fe-based PM materials

Abstract The effects of diffusion alloying on the microstructure and properties of TiC-reinforced Fe-based powder metallurgy materials were investigated via X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, and mechanical testing. The results show that the distribution of Ti in diffusion-alloyed particles becomes more uniform with increasing diffusion time. The TiC particles formed in-situ during sintering, and the microstructure of Fe-based powder metallurgy materials prepared from diffusion-alloyed powders became rounder, more uniform and refined with increasing diffusion alloying time. The apparent hardness and the bending strength increased with increasing diffusion time. The fracture mode of the samples prepared from diffusion-alloyed powders had brittle and ductile characteristics.

Influence of organic corrosion inhibitors on pickling corrosion behaviour of sinter-forged C45 steel and 2% Cu alloyed C45 steel

Good mechanical and metallurgical properties of powder metallurgy (P/M) materials made them to have limitless applications. In order to minimize corrosion rate during pickling or acid cleaning process corrosion inhibitors are used. In this research work, an attempt is made to investigate the influence of some organic inhibitors with various concentrations on acid pickling corrosion behaviour of sintered & densified C45 steel and 2% Copper addition to C45 steel with both sintered & densified conditions. Organic corrosion inhibitors Thiourea, Glycine and Sodium Benzoate were used. The specimens were subjected to acid pickling with and without organic corrosion inhibitors for 25 hours with 250 ml of 18% hydrochloric acid (HCl) as pickling medium. The weights of the specimen before and after immersion were measured using shimadzu electronic digital weighing balance. The corrosion tests were performed according to the standards. The corrosion behaviour have been analyzed with increase in pH values due to increase in concentrations of inhibitors in the acid solution. The test results were related with the SEM/optical morphology of the corroded surfaces. The corrosion resistance of the C45 steel is increased with the addition of copper. Among the inhibitors taken for investigation, Thiourea reduces the corrosion rate to maximum extent for all the compositions because of the presence of sulphides and nitrides.

Friction and wear behaviours of surface densified powder metallurgy Fe–2Cu–0.6C material

Surface rolling was employed to fabricate a densified layer on a powder metallurgy (PM) Fe–2Cu–0.6C piece. A densified surface layer with a depth of 335 μm and a surface hardness of 330 HV0.1 was obtained, in which the lamellar spacing of pearlite and grain size of ferrite were refined. Friction and wear behaviours of the surface densified material were studied. Results indicated that friction coefficient of the rolled material decreased as the load increased, which was lower than that of the un-rolled material. Wear volumes were lower than that of the un-rolled material, which increased as the load increased. Wear loss was caused by flake spalling and grooves, and the wear mechanism mainly was abrasive wear. The surface densified layer with higher hardness and lower porosity can hinder the cracks initiation and propagation on the surface and under the surface, which enhance the wear resistance of the PM material.

Corrosion Properties of Powder Bed Fusion Additively Manufactured Stainless Steels

Metal additive manufacturing (AM) has recently become a desirable process for complex parts across a broad range of applications. Laser powder bed fusion (LPBF) is an AM process for metals whereby a laser is used to selectively melt a pattern in successive layers of powder material as a means of building a three dimensional structure. The resultant material often contains pores and locally high cooling rates produced highly non-equilibrium solidification conditions which lead to solute segregation and formation of terminal solidification phases.[1,2] As a result of these varied microstructures, AM alloys may exhibit mechanical properties vastly different to their traditional wrought or cast counterparts.[3,4] While some adjustments have been made in manufacturing to enhance mechanical traits, such as incorporation of carbide particles into the powder mixture for strengthening, very little attention has been directed at understanding or enhancing the corrosion properties of these materials.[5,6] Initial studies of LPBF and powder bed injection molded steels have suggested that porosity and/or elemental segregation, similar to effects seen in more traditional powder metallurgy materials, result in varied microstructures.[7,2] These characteristics may lead to reduction in corrosion resistance of the AM stainless steels compared to their conventional, thermomechanically-processed counterparts. Studies to date have not produced results relating both the corrosion characterization of these materials in full immersion and atmospheric environments, or provided direct evidence of the possible microstructural influences on corrosion. This presentation explores the corrosion resistance of a range of LPBF stainless steels including 304L, 316L, and 17-4 PH in aqueous sodium chloride solutions. Comparison is made against their wrought plate counterparts. Samples were electrochemically characterized in both their as-printed state (image in Figure 1-a) and after grinding and polishing to a range of surface finishes. Initial potentiodynamic polarization measurements show considerable deviation between the behaviors of the AM steels vs. plate material (Figure 1-b), with about a 100 mV shortening of the passive region and up to a half order magnitude increase in the passive current density for the AM steel. This suggests influences of the porosity and microstructure of the LPBF alloy on the corrosion behavior, which may also affect these materials in the polished condition. In-situ and ex-situ characterization is being carried out to directly examine the influence of microstructural features on realized corrosion behavior. Finally, electrochemical behavior in full immersion is related to their performance in ASTM B-117 salt fog exposures as indication of their atmospheric corrosion performance. Results from this work will provide insight into the microstructural influences of AM materials on their corrosion susceptibility compared to traditional materials of the same alloys. Furthermore, the insight gained will inform processing pathways for optimization of corrosion performance. Acknowledgements Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000 References [1] L. Thijs, F. Verhaeghe, T. Craeghs, J.V. Humbeeck, and J.P. Kruth, Acta. Mater., 58 (2010) 3303. [2] M. Raza, F. Ahmad, M. Omar, and R. German, J. Materials Processing Technology, 212 (2012) 164. [3] M. Mani, B. Lane, A. Donmez, S. Feng, S. Moylan, R. Fesperman, National Institute of Standards and Technology, Gaithersburg, MD, NIST Interagency/Internal Report (NISTIR) 8036 (2015). [4] A. Wegner, G. Witt, Physics Procedia, 39 (2012) 480. [5] A. Hedge, A. Patil, and V. Tambrallimath, IJERT, 3 (2014) 14. [6] A. Poopola, Int. J. Electrochem. Sci., 9 (2014) 1273. [7] J. Trelewicz, G. Halada, O. Donaldson, and G. Manogharan, JOM, 68.3 (2016) 850. Figure 1

Ductile CoCrFeNiMox high entropy alloys strengthened by hard intermetallic phases

Face-centered-cubic (fcc) type high entropy alloys (HEAs) exhibit outstanding ductility even at the liquid nitrogen temperature, but they are relatively weak in strength which is far from the requirements for practical structural applications. One of the general concepts employed previously in alloy design is the suppression of ‘brittle’ intermetallic compound formation which usually leads to a serious embrittlement. Surprisingly, we reveal in this study that the precipitation of hard σ and μ intermetallic compounds tremendously strengthened the CoCrFeNiMo0.3 HEA but without causing a serious embrittlement. It exhibits a tensile strength as high as 1.2 GPa and a good ductility of ∼19%. A careful study of the deformation behavior reveals that the fcc matrix exhibits an extremely high work hardening exponent of 0.75, which suppresses the propagation of microcracks originated at these brittle particles. Our work presents a very successful demonstration of using complex hard intermetallic particles to manipulate the properties of fcc-type HEA systems. Furthermore, lattice distortion has been carefully measured in powder-metallurgy materials by line broadening from X-ray diffraction (XRD). It is interesting to discover that lattice planes are highly distorted in HEAs and this distortion also contributes to solid solution hardening.

Reakcijsko sintranje in zgoščevanje s plazemskim sintranjem NiAl intermetalne zlitine

This paper proposes a novel method for powder-metallurgy preparation of compact NiAl intermetallics. In the first step, the NiAl powder is prepared with the reactive-sintering procedure. The porous NiAl product of the SHS reaction is milled to a fine powder and consequently compacted by SPS processing. The compaction of powder metals and alloys is a very difficult field due to the need of preserving the unique properties of the initial materials. One of the few possible methods of a successful compaction is plasma sintering. To describe detailed structures of powder-metallurgy materials, it is necessary to use advanced microscopy methods such as SEM and TEM. In this study, the structure of a NiAl intermetallic compound is described. The material was first produced, with reactive sintering, from pure elements. Subsequently, the NiAl porous master alloy was milled and compacted with the spark-plasma-sintering (SPS) technique. The particle size of the NiAl powder was comparable to the grain size of the compacted material, which exhibited a low porosity. It was proved that the interconnection of the NiAl particles is made by a thin layer of nanocrystalline oxides.

Investigation on the Fe-based PM materials reinforced by In Situ synthesized TiC particulates

ABSTRACTAtomized iron powder, carbonyl nickel powder, molybdenum powder, electrolytic copper powder, titanium powder and graphite powder were used as experimental materials; the titanium and graphite powders were added by an atomic ratio of Ti/C = 1:1 (the addition of Ti was 0 ∼ 4 wt%) to Fe-2Ni-0.5Mo-2Cu-0.3C powder, and the iron-based powder metallurgy materials reinforced by in situ-synthesized TiC particulates were prepared by a powder metallurgy technique. The results show that the microstructures of sintered samples are mainly pearlite, ferrite and bainite. The amount of pearlite increases with the increase of Ti content, whereas the ferrite and bainite decrease. TiC particles sized 0.3 µm distribute mainly near the grain boundary of pearlite. The apparent hardness of sintered samples increases, while the sintered density and flexural strength decrease with the increase of Ti content. The fracture morphology of the sintered materials is brittle type.

PM materials selection: The key for improved performance of diamond tools

The ornamental rock processing is carried out mainly using diamond tools. These are currently being produced by powder metallurgy (PM) techniques from diamond and blend powders. In view of the diversity of materials processing routes available, natural materials, and the different processes used in rock processing, diamond tools best suited to each material require formulation of specific compositions capable to achieve suitable performances at a cost as low as possible.

Experimental Study on the Surface Densification of Fe-2Cu-0.6C Powder Metallurgy Material

The present work investigated the effects of rolling force (longitudinal feed) and spindle speed on surface performance of Fe-2Cu-0.6C powder metallurgy material. A newly self-designed rolling tool was used to densify the material's surface, and then the surface properties were measured. Results indicated that rolling force was the main effective parameter, and spindle speed was the secondary one. A densified depth and a surface hardness of 335 µm and 320 HV0.1 were obtained by using a rolling force of 2800 N and a spindle speed of 360 r/min. The tensile strength was improved by 75%. The tensile fracture had mixed-rupture characteristics of dimples and tear ridge. In the surface layer, the ferrite was stretched and refined. The pearlite was deformed and oriented along the rolling direction. The lamellar spacing close to the surface was reduced. It played a significant role in enhancing the strength of material.

Experimental investigations on welding characteristics of sinter-forged pre-alloy Atomet 4601 steel

Welding of powder metallurgy (P/M) materials continues to be challenging due to the complexities in terms of thermal and metallurgical processes as a result of porosity. Though fusion welding may reduce or totally eliminate porosity levels in the weld zone, metallurgical changes in the heat-affected zone (HAZ) and PMZ may pose problems relating to strength of the welded joints. The present research work aims to study the mechanical and metallurgical changes in a sinter-forged pre-alloy Atomet 4601 (Fe-0.54 % molybdenum (Mo)-1.8 % nickel (Ni)+0.3 %C) low alloy steel subjected to tungsten inert gas (TIG) welding. Green cylindrical compacts were sintered in a nitrogen-purged muffle furnace at a temperature of 1120 °C for 20 min and subjected to cold upsetting to get various densities of specimens. TIG welding was performed on the forged alloy steel plates with suitable filler material. The TIG-welded alloy steel was subjected to tensile and micro hardness tests, in addition to micro-examination and SEM fractographs of the fractured surfaces. Weld metal porosity has been observed in the case of parent metals with lower density. Increasing the density of alloy steel is found to enhance the tensile strength of parent metal and welded joint of alloy steels—partly due to absence of weld metal porosity. Formation of lamellar acicular ferrite at the fusion zone makes the welded joint stronger than the parent metal. The SEM image of fractured surface reveals brittle mode of fracture of the welded joint during tensile testing.

Wear Mechanisms of Hard-Brittle Material Tools in High-Speed Machining of Powder Metallurgy Material

A series of experiments was conducted in high speed machining of powder metallurgy material with PCBN tools. The main tool wear mechanisms were discussed by observing tool wear morphology utilizing scanning electron microscopy (SEM) and detecting the element distribution of the worn tool surface using energy dispersive spectroscopy (EDS).The experimental results indicate that fragile breakage occurred before it reached its blunt standard in high-speed machining of powder metallurgy material with PCBN tools,and the tools wear mechanisms are synergistic interaction among mechanical wear,binder wear and chemical wear.

Compressibility of 304 Stainless Steel Powder Metallurgy Materials Reinforced with 304 Short Stainless Steel Fibers.

Powder metallurgy (P/M) technique is usually used for manufacturing porous metal materials. However, some P/M materials are limitedly used in engineering for their performance deficiency. A novel 304 stainless steel P/M material was produced by a solid-state sintering of 304 stainless steel powders and 304 short stainless steel fibers, which were alternately laid in layers according to mass ratio. In this paper, the compressive properties of the P/M materials were characterized by a series of uniaxial compression tests. The effects of fiber content, compaction pressure and high temperature nitriding on compressive properties were investigated. The results indicated that, without nitriding, the samples changed from cuboid to cydariform without damage in the process of compression. The compressive stress was enhanced with increasing fiber content ranging from 0 to 8 wt.%. For compaction pressure from 55 to 75 MPa, greater compaction pressure improved compressive stress. Moreover, high temperature nitriding was able to significantly improve the yield stress, but collapse failure eventually occurred.

A study of the efficiency of spur gears made of powder metallurgy materials – ground versus super-finished surfaces

Power loss is one of the main concerns in gear transmission systems. In this study a recirculating power back-to-back FZG test rig was used to investigate the efficiency of spur gears made of powder metallurgy (PM) material using two different surface manufacturing methods (ground and super-finished). The results were compared with previously presented results of standard gear material from the same test rig. The influence of the material (Wrought steel or PM) and surface roughness on the gear mesh efficiency and the total efficiency of the gearbox were analyzed in detail. The Young’s modulus for PM materials is lower than for conventional gear steel. This may influence gear tooth bending and the efficiency of the gear transmission. Gear contact simulation results showed that the influence of gear tooth bending on PM gear transmission efficiency can be ignored in the FZG gear geometry. Higher surface energy combined with a smoother surface led to a lower transmission efficiency for the super-finished powder metallurgy gear combination compared to the standard gear material.

Comparison of the machinability of titanium alloy forging and powder metallurgy materials

In this paper, Ti-6Al-4V powder metallurgy (PM) material was prepared with hot isostatic pressing technology. In order to compare the machinability of the Ti-6Al-4V forging and PM materials, cutting experiments of Ti-6Al-4V forging and PM materials were done using a grooved tool involved in tool wear mechanisms, tool life, cutting temperature, cutting forces, and chip formation. In the machining of the PM material, chipping wear of the cutting tool became more severe due to the more severe microfluctuation of cutting forces, and adhesive wear turned to be slighter because of the influence of void on the tool-chip interface friction. Compared with the cutting tool average flank wear (VB) in the machining of the two materials, the tool life in the machining of the PM material was longer than that of the forging material. Taking into consideration cutting forces and cutting temperature, the better machinability was attributed to the smaller cutting forces, but the cutting temperature of the PM material was slightly higher than that of the forging material. In terms of the chip morphology, the void in the PM material made the lamella structure of the back surface more uniformly distributed and made the deformation coefficient greater.

A Study on Al<sub>2</sub>O<sub>3</sub>/SiC/B<sub>4</sub>C Reinforced Cu-Sn Matrix Composite by Warm Compaction Powder Metallurgy

Increasing density is the best way to increase the performance of powder metallurgy materials. Conventional powder metallurgy processing can produce copper green compacts with density less than 8.3g/cm3(a relative density of 93%). Warm compaction, which is a simple and economical forming process to prepare high density powder metallurgy parts or materials. CuSn matrix composites with %2 weight fractions of reinforcement particles were prepared using warm compaction and sintering. Micro-structural aspects were observed by optical microscope. Density, hardness and wear tests were also performed. Abrasion resistance measurements were used to study the abrasive behaviors of CuSn matrix and its composites. The effects of reinforcement and preparation methods on the microstructure and mechanical properties of composites have been investigated.

Liquid Phase Sintering of Boron-Containing Powder Metallurgy Steel with Chromium and Carbon

Liquid phase sintering is an effective method to improve the densification of powder metallurgy materials. Boron is an excellent alloying element for liquid phase sintering of Fe-based materials. However, the roles of chromium and carbon, and particularly that of the former, on liquid phase sintering are still undetermined. This study demonstrated the effects of chromium and carbon on the microstructure, elemental distribution, boride structure, liquid formation, and densification of Fe-B-Cr and Fe-B-Cr-C steels during liquid phase sintering. The results showed that steels with 0.5 wt pct C densify faster than those without 0.5 wt pct C. Moreover, although only one liquid phase forms in Fe-B-Cr steel, adding 0.5 wt pct C reduces the formation temperature of the liquid phase by about 50 K (°C) and facilitates the formation of an additional liquid, resulting in better densification at 1473 K (1200 °C). In both Fe-B-Cr and Fe-B-Cr-C steels, increasing the chromium content from 1.5 to 3 wt pct raises the temperature of liquid formation by about 10 K (°C). Thermodynamic simulations and experimental results demonstrated that carbon atoms dissolved in austenite facilitate the eutectic reaction and reduce the formation temperature of the liquid phase. In contrast, both chromium and molybdenum atoms dissolved in austenite delay the eutectic reaction. Furthermore, the 3Cr-0.5Mo additive in the Fe-0.4B steel does not change the typical boride structure of M2B. With the addition of 0.5 wt pct C, the crystal structure is completely transformed from M2B boride to M3(B,C) boro-carbide.

An Analysis of the Microstructure and Mechanical Properties of Rapidly Solidified Al-1Fe-1Ni-5Mg Alloy

Experiments on Al-1Fe-1Ni-5Mg alloy were performed to determine the effect of rapid solidification (RS) on the material strengthening, which result from the refining of the grain size and intermetallic compounds. Additionally, an enhancement of the material strengthening due to magnesium addition was also observed. RS procedure was performed using spray deposition of the molten alloy on the rotating water-cooled copper roll. As a result, highly refined structure of rapidly solidified flakes was obtained. Using common powder metallurgy (PM) techniques, i.e. cold pressing, vacuum degassing and hot extrusion, as received RS-flakes were consolidated to the bulk PM materials. For comparison purposes, the conventionally cast and hot extruded Al-1Fe-1Ni-5Mg alloy was studied as well. RS process combined with hot pressing and extrusion procedure was found to be very effective method for the manufacture of fine grained material and effective refinement of intermetallic compounds. However some inhomogenity of particles distribution was observed, which was ascribed to varied cooling rate dependent on the particular spray-drop size. Mechanical properties of as-extruded material were examined using compression test at 293K – 873K. High strength and ductility of as-extruded RS material with respect to conventionally produced alloy were observed. However, the effect of enhanced mechanical properties of RS material is observed only at low deformation temperatures. It was found that increasing deformation temperature above 400K results in negligible hardening of RS samples if compared to conventionally produced material.

Stochastic characteristics of powder metallurgy processing

Stochastic characteristics of powder metallurgy processing are analyzed. Theoretical formulation is described which presents probabilistic distributions of material constituents. The described method is based on Poisson processes. Examples of stochastic characteristics of powder metallurgy processing are presented and discussed. The results derived can be used for evaluation of powder metallurgy materials and the subsequent quantitative stochastic design as well as stochastic optimization of powder materials and powder processing.