The effect of FeS film on the surface of iron powder particles on mechanical properties and fracture of Fe–Cu–C alloys

This article provides a new kind of P/M processing by designing thin-layered FeS film coated on the surface of iron powder particles for preparing high density Fe–Cu–C materials. Experimental results showed that FeS lubricating coating on the surface of iron powder particles was significant as a means of reducing friction in the pressing process of Fe–Cu–C alloys. After being pressed, the green density increased from 7.18 to 7.42?g?cm^?3. The sintered density increased from 7.10 to 7.37?g?cm^?3. In the sintering process, the FeS was liquid, and useful in purifying particle surface and strengthening grain boundaries to improve the mechanical properties. The hardness and tensile strength of the Fe–2.0Cu–0.9C–0.5FeS₂ material were 80.5 HRB and 590?MPa. Analysis of fracture showed the main fracture was transgranular fracture. And FeS spherical particles gathered in the pores of the Fe–Cu–C alloys.     

Effect of Lead Addition and Milling on Densification and Mechanical Properties of 6061 Aluminium Alloys

In the present work, one batch of prealloyed 6061Al powder was mixed with different lead compositions (5, 10, 15 vol.%) and another set with same composition was ball-milled for 5 h at 300 rpm. Microstructural features such as lattice constant, crystallite size, particle size and morphology were studied using XRD, particle size analyzer and SEM. Both the as-mixed as well as ball-milled powders were compacted at 300 MPa and sintered under N₂ atmosphere for 1 h in tube furnace at 590 °C. The ball milling of 6061Al alloy powder improved sinter density and densification while lead addition showed negligible influence on these parameters. The microstructure of as-mixed 6061Al–Pb alloys exhibited equiaxial morphology whereas ball-milling resulted in elongated grains with uniform lead distribution. Quasi-static compressive mechanical behavior was investigated for 6061Al–Pb alloys at 1 × 10^?3 s^?1 strain rate. Results indicated that ultimate compressive and yield strength were sensitive to milling and lead volume fraction.     

Fabrication,microstructures and properties of 50 vol.-% SiCp/6061Al composites via a pressureless sintering technique

Commercial F500 SiC powder and 6061 Al powder were chosen to fabricate the 50?vol.-% SiCp/6061Al composites via pressureless sintering. Effects of pre-treatment of the SiC powder and sintering temperature on the microstructures and properties of the composites were studied. Densification mechanism and interfacial reaction of the composites were also investigated. The results show that the composites have a high sintering ability and a low interfacial reaction activity. The density, bending strength and thermal conductivity of the composites are all sensitive to the sintering temperature. The composites sintered at 680°C are nearly fully dense and have the following optimal properties: the relative density of 98.5%, the bending strength of 495?MPa, the TC of 153?W/(m?K) and the coefficient of thermal expansion of 8.1?×?10^?6/°C (50–100°C), which are superior to most of the SiCp/Al composites of the similar composition reported previously.     

Mechanical alloying and field assisted hot pressing of nanocrystalline B2-NiAl intermetallic compound

Abstract

Ordered B2-NiAl intermetallic compound powder was successfully synthesised by mechanical alloying after 20 h in an attritor mill, starting from elemental Ni and Al powders and without subsequent heat treatment. NiAl powder obtained was homogenous and had a nanocrystalline microstructure. It was consolidated by field assisted hot pressing (FAHP), in a novel configuration with a Gleeble 3800 thermomechanical simulator. The powder was also processed by hot isostatic pressing (HIP) in order to compare both methods. The consolidation was successful by both methods obtaining above 98% of NiAl theoretical density (5·86 g cm^?3). The results showed that the consolidation process by FAHP technique is effective and uniform throughout the sample as indicated by homogenous hardness values, obtaining microstructure and properties similar to those obtained with HIP technique, with certain advantages over it. The achieved room temperature yield strength of 850 MPa and fracture strain 26–28% corresponds to the bulk values of NiAl intermetallic.     

Study on microstructure and mechanical properties of spark plasma sintered Alumix 431 powder

Spark plasma sintering (SPS) has been used to successfully densify a 7075 aluminium alloy obtained from Alumix 431 powder. Sintering experiments were conducted at the temperature of 450 and 500°C for 2.5, 5 and 10?min. All the presented results confirm the excellent sinterability of Alumix 431 powder in vacuum during the SPS process and clearly show the effect of sintering temperatures and holding times on the densification, microstructure and mechanical properties of the obtained sintered compacts. The best results of hardness (1412?±?39?MPa), tensile strength (345?±?15?MPa) and compressive strength (618?±?4?MPa) were obtained by the compacts sintered at 500°C for 5 min.     

Dynamic compaction of titanium Aluminides by Explosively Generated Shock Waves: Microstructure and Mechanical Properties

A detailed microstructural analysis and evaluation of the mechanical properties of titanium aluminides consolidated by novel shock processes^[131] are presented. Successful consolidation was obtained and was evidenced by strong bonding between individual particles. Additions of Nb and Ti and Al elemental powders resulted in enhanced interparticle bonding through intense plastic deformation of Nb and shock-induced reactions between Ti and Al. Rapid cooling of interparticle molten layers yielded amorphous Ti-Al alloys; this interparticle melting and rapid cooling are a unique feature of shock processing. Embrittlement of individual particles of Ti₃Al-based alloy after exposure to 550 °C and 750 °C was observed. There is evidence of phase transformation after preheating the powder, and this fact can explain the high density of cracks obtained with this alloy after high-temperature shock consolidation. Mechanical properties of the Ti₃Al-based alloy were determined at room temperature and the fracture modes were studied. The microstructural observations are correlated with the mechanical properties.     

Dynamic compaction of titanium aluminides by explosively generated shock waves: Microstructure and mechanical properties

A detailed microstructural analysis and evaluation of the mechanical properties of titanium aluminides consolidated by novel shock processes^[13] are presented. Successful consolidation was obtained and was evidenced by strong bonding between individual particles. Additions of Nb and Ti and Al elemental powders resulted in enhanced interparticle bonding through intense plastic deformation of Nb and shock-induced reactions between Ti and Al. Rapid cooling of interparticle molten layers yielded amorphous Ti-Al alloys; this interparticle melting and rapid cooling are a unique feature of shock processing. Embrittlement of individual particles of Ti₃Al-based alloy after exposure to 550 °C and 750 °C was observed. There is evidence of phase transformation after preheating the powder, and this fact can explain the high density of cracks obtained with this alloy after high-temperature shock consolidation. Mechanical properties of the Ti₃Al-based alloy were determined at room temperature and the fracture modes were studied. The microstructural observations are correlated with the mechanical properties.     

Spark Plasma Sintering of Cryomilled Nanocrystalline Al Alloy - Part II: Influence of Processing Conditions on Densification and Properties

In this study, nanostructured Al 5083 powders, which were prepared via cryomilling, were consolidated using spark plasma sintering (SPS). The influence of processing conditions, e.g., the loading mode, starting microstructure (i.e., atomized vs cryomilled powders), sintering pressure, sintering temperature, and powder particle size on the consolidation response and associated mechanical properties were studied. Additionally, the mechanisms that govern densification during SPS were discussed also. The results reported herein suggest that the morphology and microstructure of the cryomilled powder resulted in an enhanced densification rate compared with that of atomized powder. The pressure-loading mode had a significant effect on the mechanical properties of the samples consolidated by SPS. The consolidated compact revealed differences in mechanical response when tested along the SPS loading axis and radial directions. Higher sintering pressures improved both the strength and ductility of the samples. The influence of grain size on diffusion was considered on the basis of available diffusion equations, and the results show that densification was attributed primarily to a plastic flow mechanism during the loading pressure period. Once the final pressure was applied, power law creep became the dominant densification mechanism. Higher sintering temperature improved the ductility of the consolidated compact at the expense of strength, whereas samples sintered at lower temperature exhibited brittle behavior. Finally, densification rate was found to be inversely proportional to the particle size.     

Liquid-phase sintering of TiN-enriched T15-grade high-speed steels and their mechanical properties

The present investigation is an attempt to develop composites based on high-speed steel through liquid-phase sintering route using a powder metallurgical technique. Water-atomised annealed T15-grade HSS powder, lubricant and various mass percents of TiN (0–8%) were blended and axially compacted into green pellets at 850 MPa at room temperature. During sintering studies carried out in vacuum (10^?2 torr), optimum temperature for full densification was determined for each composition. Only full dense sintered samples (density ≥98% theoretical) were selected for further heat treatment and the evaluation of mechanical properties. Mechanical properties like hardness, transverse rupture strength and hot compressive yield strength were evaluated. Both qualitative and quantitative metallographic studies were carried out and chemical analysis of various phases in sintered as well as heat-treated composites were determined using SEM-EDX. The results confirm that fully dense composites containing up to 2% TiN exhibit equivalent mechanical properties, although some differences in service behaviour e.g. wear resistance are to be expected.     

Sintering Behaviour and Mechanical Properties of Al–Cu–Mg–Si–Sn Aluminum Alloy

The present study investigates the effect of compaction pressure and sintering temperature on densification response and mechanical properties of the Al–3.8Cu–1Mg–0.8Si–0.3Sn (2712) alloy. The compacts were pressed at 200 and 400 MPa and sintered at temperatures ranging from 570–630°C in vacuum (10^?6 Torr). The objective of the present work is to obtain an optimum sintering conditions for achieving higher sintered densities and mechanical properties. The effect of sintering temperature is evaluated by measuring the sintered density, densification parameter, microstructure, phase changes and mechanical properties. While a higher sintering temperature results in densification enhancement, it also leads to microstructural coarsening. Significant improvement in mechanical properties is obtained through age-hardening of sintered alloy under various ageing conditions (T4, T6 and T8).     

Al-Fe-Ce alloys based on water-atomized powders for high-temperature applications

The microstructure and mechanical properties of Al-Fe-Ce alloys based on water-atomized powders between 20 and 300 °C are examined in comparison with the properties of similar alloys produced by other rapid crystallization techniques. Changes in atomization parameters vary both the cooling rate (from 10⁴ to 10⁶ K/sec) and powder size distribution (from 5 to 100 µm). The excellent compactability of water-atomized powders facilitates powder consolidation, which is based on hot extrusion and cold pressing of degassed powders. The mechanical properties are examined by tensile tests. The ultimate tensile strength is 500 to 550 MPa at 20 °C and 270 to 300 MPa at 300 °C at adequate plasticity. The properties achieved are comparable with those of similar alloys known from the literature.     

Powder injection moulding of Inconel 713C alloy

ABSTRACT

To find a proper super alloy applied to gasoline engine turbochargers which demand a high operating temperature over 950°C, the IN713C super alloy was investigated in this study. The rheological properties of feedstock, density, microstructure and mechanical properties were measured. The proper powder loading was 61?vol.-%. Through the analysis of viscosity, 160°C was supposed to be more suitable for the injection. After debinding, most binder components were removed. A reasonable debinding process was formulated. Two pre-sintering temperature (850, 950°C) were investigated, then 850°C was considered to be more proper relatively. The samples were sintered at different temperatures for various time. The best properties of sintered parts were obtained when sintered at 1300°C for 3?h, the density of sintered parts was 7.83?g?cm^?3 while the hardness was 43.6 HRC and tensile strength was 1216.9?MPa.     

Microstructural Evolution and Mechanical Properties of Nanointermetallic Phase Dispersed Al<Subscript>65</Subscript>Cu<Subscript>20</Subscript>Ti<Subscript>15</Subscript> Amorphous Matrix Composite Synthesized by Mechanical Alloying and Hot Isostatic Pressing

The structure and mechanical properties of nanocrystalline intermetallic phase dispersed amorphous matrix composite prepared by hot isostatic pressing (HIP) of mechanically alloyed Al₆₅Cu₂₀Ti₁₅ amorphous powder in the temperature range 573 K to 873 K (300 °C to 600 °C) with 1.2 GPa pressure were studied. Phase identification by X-ray diffraction (XRD) and microstructural investigation by transmission electron microscopy confirmed that sintering in this temperature range led to partial crystallization of the amorphous powder. The microstructures of the consolidated composites were found to have nanocrystalline intermetallic precipitates of Al₅CuTi₂, Al₃Ti, AlCu, Al₂Cu, and Al₄Cu₉ dispersed in amorphous matrix. An optimum combination of density (3.73 Mg/m³), hardness (8.96 GPa), compressive strength (1650 MPa), shear strength (850 MPa), and Young’s modulus (182 GPa) were obtained in the composite hot isostatically pressed (“hipped”) at 773 K (500 °C). Furthermore, these results were compared with those from earlier studies based on conventional sintering (CCS), high pressure sintering (HPS), and pulse plasma sintering (PPS). HIP appears to be the most preferred process for achieving an optimum combination of density and mechanical properties in amorphous-nanocrystalline intermetallic composites at temperatures ≤773 K (500 °C), while HPS is most suited for bulk amorphous alloys. Both density and volume fraction of intermetallic dispersoids were found to influence the mechanical properties of the composites.     

Sintering and magnetocaloric properties of gas atomised LaFe11.0Si1.2Co0.8

ABSTRACT

The sintering behaviour of LaFe_11.0Si_1.2Co_0.8 powder produced by gas atomisation was examined to provide a basis for the application of powder metallurgical shaping technologies to magnetocaloric La(Fe,Si)₁₃-alloys. The aim was to establish sintering parameters for attaining both high densification and good magnetocaloric properties for the investigated particle sizes <10 µm and <25?µm. Dilatometry measurements and sintering trials were carried out and density, microstructure and entropy change ΔS of the sintered samples were analysed. For the fine particles <10?µm, the lowest investigated sintering temperature 1150°C results in a relative density of 97%, a low α-Fe content and a high ΔS?=??5?J?kg^?1?K^?1 (ΔH=2?T). For powder <25?µm, a two-stage process is required to achieve similar properties.     

Sintering of Tungsten and Tungsten Heavy Alloys of W–Ni–Fe and W–Ni–Cu: A Review

Tungsten is a refractory metal possessing good mechanical properties of high strength, high yield point, and high resistance to creep. Therefore, tungsten and its alloys are used in many high temperature applications. Due to the high melting point, they are generally processed through powder metallurgy method. The powders are compacted using die pressing or isostatic pressing. The compacts are sintered in a sintering furnace to achieve high density, thereby, making the metal suitable for further processing. This article reviews the recent research findings of consolidating tungsten and its alloys (W–Ni–Fe and W–Ni–Cu), from preparation of powder alloys to sintering of the compact. The advances in sintering are based on the objective of achieving good densification of the metal at lower temperature and at faster rate. The use of microwave sintering and spark plasma sintering techniques resulted in significant reduction in sintering time and producing products of good mechanical properties.     

Sintering of maraging steel with phosphorous additions

Abstract

The aim of this study was to develop a steel powder system for rapid tooling applications. The properties required are rapid densification, dimensional precision, high mechanical strength and corrosion resistance. To this end, the densification and microstructural development of a loose packed 200 grade maraging steel powder sintered with ferrophosphorous additions was examined. Liquid initially formed from a reaction of the Fe₃P and carbon, which was a residue of the polymeric binder used to shape the powder compact. This liquid caused a burst of sintering which ceased as the liquid dissipated. On further heating, a phosphorous rich supersolidus liquid appeared at triple points and grain boundaries leading to rapid densification and a sintered density of 98%.     

On hot deformation of aluminium–silicon powder metallurgy alloys

Abstract

The growing field of aluminium powder metallurgy (PM) brings promise to an economical and environmental demand for the production of high strength, light weight aluminium engine components. In an effort to further enhance the mechanical properties of these alloys, the effects of hot upset forging sintered compacts were studied. This article details findings on the hot compression response of these alloys, modelling of this flow behaviour, and its effects on final density and microstructure. Two aluminium–silicon based PM alloys were used for comparison. One alloy was a hypereutectic blend known as Alumix-231 (Al–15Si–2·5Cu–0·5Mg) and the second was an experimental hypoeutectic system (Al–6Si–4·5Cu–0·5Mg). Using a Gleeble 1500D thermomechanical simulator, sintered cylinders of the alloys were upset forged at various temperatures and strain rates, and the resulting stress–strain trends were studied. The constitutive equations of hot deformation were used to model peak flow stresses for each alloy when forged between 360 and 480°C, using strain rates of 0·005–5·0 s^?1. Both alloys benefited from hot deformation within the ranges studied. The experimental alloy achieved an average density of 99·6% (±0·2%) while the commercial alloy achieved 98·3% (±0·6%) of its theoretical density. It was found that the experimentally obtained peak flow stresses for each material studied could be very closely approximated using the semi-empirical Zener–Hollomon models.     

On development of press and sinter Al–Ni–Mg powder metallurgy alloys

Abstract

The objective of this research was to initiate the development of powder metallurgy alloys based on the Al–Ni–Mg system. In doing so, binary (Al–Mg) and ternary (Al–Ni–Mg) blends were prepared, compacted and sintered using elemental and master alloy feedstock powders. Research began with fundamental studies on the sintering response of the base aluminium powder with additions of magnesium. This element proved essential to the development of a well sintered microstructure while promoting the formation of a small nodular phase that appeared to be AlN. In Al–Ni–Mg systems a well sintered structure comprised of α aluminium plus NiAl₃ was produced at the higher sintering temperatures investigated. Of these ternary alloys studied, Al–15Ni–1Mg exhibited mechanical properties that were comparable with existing commercial 'press and sinter' alloys. The processing, reaction sintering and tensile properties of this alloy were also found to be reproducible in an industrial production environment.     

Spark plasma sintering versus hot pressing – densification,bending strength,microstructure, and tribological properties of Ti5Al2.5Fe alloys

Ti5Al2.5Fe alloys were fabricated by the spark plasma sintering (SPS) and hot pressing (HP) pressure-assisted sintering techniques from pre-alloyed powders with a particle size of about 200?μm. The powders were sintered at 850 °C for two different holding times (5 and 8 min) and heating rates (50 and 150°C?min^?1) at 25?MPa. The maximum relative densities were 99.70 and 98.78% for SPS and HP samples, respectively. All the alloys prepared by the SPS process had significantly higher bending strengths (1825–2074?MPa) than the alloys prepared by the HP process (648–1330?MPa). A decrease in the heating rate from 150 to 50°C min^?1 enhanced the wear resistance of the Ti5Al2.5Fe alloys prepared by both the SPS and HP processes.     

Microstructural and mechanical properties of injection moulded gas and water atomised 17-4 PH stainless steel powder

Abstract

This paper describes the microstructural and mechanical properties of injection moulded 17-4 PH stainless steel gas and water atomised powder. Gas and water atomised stainless steel powders were injection moulded with wax based binder. The critical powder loading for injection moulding were 62·5 and 55 vol.-% for gas and water atomised powders respectively. Binder debinding was performed using solvent and thermal method. After dedinding the samples were sintered at different temperatures for 1 h in pure H₂. Metallographic studies were conducted to determine to extend densification and the corresponding microstructural changes. The results show that gas atomised powder could be sintered to a maximum (98·7%) of theoretical density, and water atomised powder could be sintered to a maximum (97·08%) of theoretical density. Maximum tensile strength was obtained for gas atomised powder sintered at 1350°C. The tensile strength of the water atomised powder sintered at the same temperature was lower owing to higher porosity. Finally, mechanical tests show that the water atomised powder has lower mechanical properties than gas atomised powder.