Powder Metallurgical Method Research Articles

Effect of Boron on Microstructure and Fracture of Sintered Ultrafine-Grained Tungsten

Ultrafine-grained tungsten shows strong potential for ballistic applications because of its increased strength, and higher propensity for strain localization compared with coarse-grained materials. However, tungsten typically exhibits poor ductility at room temperature and fractures by a brittle intergranular mechanism. This study evaluates the effects of boron as a sintering aid and grain-boundary strengthening additive for ultrafine-grained tungsten prepared by powder metallurgical methods. While boron did not improve the sinterability of nanocrystalline tungsten in this study, low concentrations of boron delivered a notable increase in strength, accompanied with a transition from intergranular to transgranular fracture. These significant changes in fracture behavior show promise for improving the low-temperature ductility of tungsten; however, the corresponding improvements to plastic strain to failure were less significant than anticipated.

Comparative Study of Al-TiB2 Composite Fabricated by Different Powder Metallurgical Methods

Aluminium Metal Matrix Composites (AMMCs) are the new class of materials substituting many industrial materials. It is due to its superior qualities compared to conventional materials. AMMCs has found a versatile application because it has aluminium in matrix phase hence light in weight and also it can acquire different properties as per reinforcements used. Sintering is one of the prominent methods used to manufacture AMMCs. Sintering process is used in Powder Metallurgy in which small powdered particles are heated to bond together. The process enhances the strength as well as other mechanical and tribological properties. The technology enables us to shape materials difficult to machine, parts with complex geometries, materials having high melting point, parts with close dimensional tolerances, or to combine different materials which is not possible with any other process. The most important part is that the density of the product can be controlled according to the requirements and thus self-lubricating and wear-resistant parts are possible. The present study has attempted to see if TiB2 can be used as reinforcement in AMMCs produced through powder metallurgy route and the changes in the properties of AMMCs by the different sintering methods adopted. The compacted preforms of varying compositions of reinforcement were prepared and sintered through three different methods i.e. Microwave sintering, Conventional sintering and Hot-pressing to study the changes in the properties. A comparative study has been done between the three sintering methods to see the limitations and scope for improvement.

Synthesis and characterization of alumina-CNT membrane for cadmium removal from aqueous solution

We report a simple approach for synthesizing an alumina-carbon nanotube (Al2O3-CNT) composite membrane through a powder metallurgical method. The membrane was fabricated via uniaxial pressing of the composite powder mixture and subsequent solid-state, pressure-less sintering. Homogeneous dispersion of the CNTs within the alumina matrix was achieved by using gum arabic and sodium dodecyl sulfate as dispersants. The phase composition and microstructure of the synthesized membrane were characterized using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM), respectively. The effect of process parameters (i.e., initial compaction load and sintering temperature) on the porosity, strength, and water flux of the membrane was investigated, and the results highlighted a strong influence of the process parameters on these properties. In particular, when the compaction load and sintering temperature were increased from 50 to 200 kN and 1200 to 1500 °C, the porosity of the membrane decreased from 65% to 31% and its strength increased from 0.76 to 15.64 MPa respectively. Finally, batch adsorption experiments were used to determine the cadmium removal efficiency of the alumina and CNTs adsorbents, as well as that an Al2O3-CNT powder mixture, whereas the efficiency of the membrane based on the above mixture was assessed using a flow loop system. The membrane removed 93% of the Cd present in a water solution containing 1 ppm Cd at pH 6.

Microstructures and mechanical properties of in situ TiC\u2013\u03b2\u2013Ti\u2013Nb composites with ultrafine grains fabricated by high-pressure sintering

In this study, an in situ β–Ti–Nb composites reinforced with TiC particles with an ultrafine grain size were fabricated using a powder metallurgical (PM) method. The microstructures and mechanical properties of the composites were characterized using X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and compression tests. TiC particles were formed in the ball-milled powders after annealing at 600 °C due to a chemical reaction between stearic acid and titanium. Using high-pressure sintering (HPS) on an apparatus with six tungsten carbide anvils, a fully dense β–Ti–Nb composite reinforced with fine in situ TiC particles was obtained. The TiC particles exhibit particle sizes of ~500 nm, uniformly distributed in the composite matrix, which had grain sizes of ~600 nm. Thus, the TiC–β–Ti–Nb composite show very high compression yield strength and relatively high plasticity contributed by grain refinement and TiC particles strengthening. The composite with 45 vol.% TiC exhibited excellent mechanical properties, with a yield compressive strength of 1990 MPa and plastic strain of 9.12%. More over, a modified rule-of-mixture (ROM) was presented to describe the combined strengthening effect of grain refinement and TiC particles.

Deformation and fracture characteristics of Al6092/SiC/17.5p metal matrix composite sheets due to heat treatments

In metal matrix composite (MMC) materials, the reaction between the metal matrix and reinforcement particles could change the composition of the matrix and the interface and lead to interfacial compounds. These intermetallic compounds may have either a deleterious effect to the mechanical properties or beneficial effect in enhancing the toughness and ductility of the composite. An aluminium 6092 alloy with 17.5% volume fraction silicon carbide (SiC) particles sheet manufactured by means of powder metallurgical method, heat treated to T6 condition, is used to obtain a fundamental understanding of the heat treatment effect on the fracture mechanism, the microstructural changes and the interface between the Al-matrix and SiC particles. Changes in the microstructure of the Al/SiCp and the topography of the fracture are investigated using scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM) to characterize the precipitate and intermetallic compounds formed at the Al/Sic interface. X-ray diffraction (XRD) is utilized to characterize the phase formation and to give confidence in the results of TEM and EDS. Tensile tests with different strain rates (8 × 10−5, 8 × 10−4, 8 × 10−3, 8 × 10−2 and 0.16 s−1) were carried out to study the toughness and to find a correlation between the strain rate and heat treatment. Under T6 condition, the results show that the mechanical property of this MMC is less ductile due to the formation of precipitations as a result of either the interaction between the Al and SiCp or from hardening precipitation treatment, e.g. Al2Cu, Al4Cu2Mg8Si7 and MgAl2. O-condition annealing can reduce the detrimental effect of the intermetallic compounds in the interface region and improve the toughness and ductility of the material by decreasing the intermetallic compound (Al2Cu). However, the Al/SiC sheet treated with O-condition annealing is more sensitive to the strain rate than the one treated with T6.

Thermophysical properties of sintered aluminum-silicon

The effect of silicon addition to aluminum on the thermophysical properties of Al was experimentally investigated. Thermal diffusivity, heat capacity, density, and thermal expansion of sintered Al-Si samples with Si content ranging 0–8 wt% were measured. For U-Mo/Al dispersion fuel for research reactors, an addition of Si (up to 8 wt% Si) to the Al matrix has been adopted as a method to reduce the formation of interaction layer between the U-Mo and the Al. In this study, the Si-added Al matrix was simulated by using a powder metallurgical method, in which an Al powder and a Si powder were mixed and sintered. All measured properties decreased with the addition of Si. The effect was most pronounced in thermal diffusivity while the decreases in heat capacity and density were relatively insignificant. The measured thermal conductivity from the present study was higher than those measured data for alloy samples available in the literature to the differences in the fabrication method. All measured data including this study, however, were lower than the prediction by the Bruggeman model. It is because the model assumes an ideal heat-transfer conditions such as spherical particles, homogeneous particle distribution, perfect bonding between Al and Si.

Transition in microstructural and mechanical behavior by reduction of sigma-forming element content in a novel high entropy alloy

A novel CrFeMoVMnx high entropy alloy (HEA) system was devised after screening done with thermodynamic constraints. The Mn content was varied (x=0, 0.5, 1 atomic ratio), with other elements kept in equiatomic ratios, to determine the effect of paired sigma-forming element (PSFE) content on microstructural and mechanical behavior. Alloys were successfully fabricated using a powder metallurgical method after mechanical alloying (MA) for an optimized minimum milling time. The milled powder was sintered using spark plasma sintering (SPS). The microstructural analysis indicated the appearance of a σ phase in the equiatomic quinary CrFeMoVMnx system, and the volume fraction of the σ phase varied directly by Mn content. The Mn0 system exhibited the formation of a single phase solid solution. The failure of thermodynamic prediction, the role of PSFE content and Md¯ in σ phase appearance were investigated. The transition in mechanical behavior through a reduction in Mn content was also investigated and Mn1 exhibited the highest fracture strength, of 3183MPa, and hardness of 868 Hv, while Mn0 displayed the highest plasticity. This study demonstrates higher specific yield strength and hardness values compared to previously reported HEA systems.

The Influence of Temperature on Stability of Aluminum Foam Cell Wall during Foaming Process

This study concerns about the influence of foaming temperature which is applied to foaming process of aluminum foam to improve the stability of aluminum foam cell wall. Powder metallurgical method with four major foaming temperatures of 750°C, 800°C, 850°C and 900°C have been selected. Furthermore, the porosity of the foam was determined by ImageJ Analysis Software. Microhardness testing on the cell wall of aluminium foam was conducted according to ASTM E 92 using microhardness tester LM24AT with 200 grams and 15 s for loading time. The universal testing machine was applied to characterize the effect of foaming temperature on compression strength. The aluminum foam was observed in macroscopic and microscopic level using optical microscope (OM). The result revealed that the foaming temperature of 800°C gave the lowest value of porosity, with the highest hardness and compressive strength of 55.29 HV and 1.41 MPa, respectively. In addition, the highest porosity level was acquired by foaming temperature which was set at 900 °C. The lowest hardness value of 38.50 HV was obtained by foaming temperature of 700°C and the minimum compressive strength value of 0.75 MPa was exhibited when the foaming temperature was set at 900°C.

High entropy alloy binders in gradient sintered hardmetal

High Entropy Alloys (HEAs) are a new group of multicomponent alloys showing great potential as bulk alloys in many fields, and their high temperature strength is especially of interest. In previous work (D. Linder, M.Sc Thesis “High Entropy Alloys — Alternative binders in cemented carbides”, Linköping University, Sweden (2015)) we have shown the possibility to produce cemented carbides with HEA-binders using standard powder metallurgical methods. The present work investigates the possibility to produce gradient sintered cemented carbides using HEA-binders. The materials are analyzed with regards to gradient depth, phases formed, phase composition and carbide grain size. The gradient formation is investigated with respect to C-content and sintering process and the results are showing the possibility to form industrially relevant gradient depths using standard methods. These results open up a whole new range of possible applications for these materials and show the potential for future design of a wide composition range of alternative binders.

Effect of Ball Milling Time on Microstructure and Hardness of Porous Magnesium/Carbon Nanofiber Composites

Porous magnesium/carbon nanofiber composites were produced using a powder metallurgic method to study the effect of ball milling time on their microstructure and hardness. Three ball milling times (240 min, 320 min, and 480 min) and two carbon nanofiber concentrations (0.05% and 1%) were utilized in the production of these porous composites. The increase of ball milling time led to the gradual decrease of the average size of magnesium powders from the initial 40 µm to about 26 µm after 480 min of ball milling. The powder size range first increased with the increase of ball milling time from 240 min to 320 min, and then decreased with the further increase of ball milling time to 480 min. Among the three ball milling times, the produced porous composites from the powders after 320 min of ball milling have the largest average pore size. With the increase of ball milling time from 240 min to 320 min and then to 480 min, the average Vickers microhardness data first decreased and then increased for Mg-1%C porous composites along the cross-sections parallel to the compact processing direction, increased for the cross-sections perpendicular to the compact processing direction for Mg-1%C porous composites, first increased and then decreased for the cross-sections parallel to the compact processing direction for Mg-0.05%C porous composites, and slightly decreased for the cross-sections perpendicular to the compact processing direction for Mg-0.05%C porous composites.

Preparation and characterization of iron/β-tricalcium phosphate bio-cermets for load-bearing bone substitutes

Abstract Ceramic-metal composite materials, namely cermets, are provided with characteristics of both ceramic and metal. Herein, for the first time bio-cermets based on β-tricalcium phosphate (β-TCP) bioceramic with biodegradable iron being reinforcement phase, were fabricated using the powder metallurgic method. The phase composition, microstructure, mechanical properties and in vitro cell behaviors of bio-cermets were investigated. The results revealed that atomic diffusion occurred between the iron and β-TCP matrix during the sintering process. The bio-cermets attained remarkable increase in fracture toughness (1.16–1.55 MPa m1/2) compared to the β-TCP bioceramic (0.54 MPa m1/2). The bio-cermets with 10 vol% iron showed the highest compressive strength (640 MPa), significantly higher than that of plain β-TCP bioceramic (285 MPa). The in vitro cell behaviors test indicated that the bio-cermets did not showed any sign of toxicity; the iron ions released from bio-cermets up-regulated bone-related gene expression of bone mesenchymal stem cells. The bio-cermets developed in this study represent potential bone substitutes for application in the load-bearing bone defects.

Green photoluminescence in Tb3+-doped ZrO2 nanotube arrays

Tb3+-doped ZrO2 nanotube arrays were fabricated by anodizing Zr–Tb (3 at.% Tb) alloy, which was prepared through a powder metallurgical method. The effects of electrolyte and annealing temperature on the morphologies, structures, photoluminescence properties and decay times of the nanotube arrays were studied. The nanotubes prepared from aqueous electrolyte is of tetragonal ZrO2, while the nanotubes prepared from organic electrolyte (formamide and glycerol) is of amorphous structure that can be converted to monoclinic ZrO2 after annealing at 600 °C. Under an excitation wavelength of 263 nm, the nanotubes annealed at 400 °C display a strong photoluminescence emission at 544 nm which is associated with 5D4–7F5 transitions of Tb3+. The tetragonal ZrO2 in the nanotubes was revealed to be beneficial for the improvement of the luminous efficiency and decay time.

Fabrication of Ta2O5 Dispersion-Strengthened Mo-Si-B Alloy by Powder Metallurgical Method

In this study, we investigate the effect of oxide dispersion strengthening on mechanical properties by dispersion of nano-sized Ta2O5 particles in Mo-Si-B alloy. A Mo-Si-B core-shell powder consisting of two intermetallic compounds of Mo5SiB2 and Mo3Si as the core and nano-sized Mo solid solution surrounding intermetallic compounds was fabricated by chemical vapor transport. And Mo-Si-B core-shell powder with uniformly dispersed nano-sized Ta2O5 particles on the surface of a Mo solid solution shell was produced by a wet blending process with TaCl5 solution and heat treatment. Then, pressureless sintering was performed at 1400°C for 3 h under a H2 atmosphere. The hardness and fracture toughness of the Ta2O5-dispersed Mo-Si-B alloy were measured using Vickers hardness and 3-point bending tests, respectively. The Vickers hardness and fracture toughness of the fabricated Mo-Si-B-Ta2O5 alloy were more improved than that of the Mo-Si-B alloy fabricated using core-shell powder with no addition of Ta2O5 particles (Mo-Si-B alloy: 353 Hv, 13.5 MPa·√m, Mo-Si-B-Ta2O5 alloy: 509 Hv, 15.1 MPa·√m).

Mechanical properties of Mo-Nb-Si-B quaternary alloy fabricated by powder metallurgical method

Mo-Si-B alloys composed of two intermetallic compound phases (Mo5SiB2 and Mo3Si) and a molybdenum solid solution matrix phase have been investigated for use as high-temperature structural materials due to their high melting point and good creep resistance. However, despite these advantages, Mo-Si-B alloys are difficult to use in practical applications because they have insufficient fracture toughness at room temperature. So, in many researches, microstructure control and the addition of other elements in the α-Mo matrix phase are conducted as an effective way to improve the fracture toughness.In this study, niobium (Nb) was added to a Mo-Si-B alloy by a powder metallurgical method to improve the mechanical properties. First, the Mo and Nb powders were pulverized by high-energy ball milling. Then, the synthesized intermetallic compound powders, which were fabricated by continuous heat treatment under a H2 atmosphere, were mixed with ball-milled Mo and Nb powder. Pressureless sintering was conducted at 1400°C for 3h under a H2 atmosphere. The Vickers hardness and fracture toughness were measured to investigate the mechanical properties of the sintered Mo-Si-B and Mo-Nb-Si-B alloy. The Vickers hardness was about 425Hv for a Mo-Nb-Si-B alloy, which was lower value of 165Hv compared to Mo-Si-B alloy (590Hv). On the other hand, the fracture toughness of the Mo-Nb-Si-B alloy (14.5MPa·√m) greatly increased compared to that of the Mo-Si-B alloy (12.6MPa·√m).

Effect of TiC addition on the microstructure and mechanical properties of TiN-based cermets

In this paper, the influence of TiC addition on the microstructure and mechanical properties of TiN-based cermets fabricated through the powder metallurgical method was systematically investigated by scanning electron microscopy, X-ray diffraction and mechanical tests. The results showed that the TiC content had a significant effect on the microstructure evolution and mechanical properties of TiN-based cermets. When the added TiC content increased from 0 to 20wt%, the transverse rupture strength, relative density and fracture toughness increased initially, exhibited a maximum and then decreased, while the hardness increased monotonically. As the TiC content was 10wt%, the transverse rupture strength, relative density, fracture toughness and Rockwell hardness of TiN-based reached up to 2223MPa, 99.87%, 15.7MPam1/2 and 88.7HRA, respectively.

Preparation and photoluminescence properties of Tm3+-doped ZrO2 nanotube arrays

Tm3+-doped ZrO2 nanotube arrays were prepared by anodization of a Zr–Tm alloy (3 at.% Tm) obtained by a powder metallurgical method. The morphologies, structures, elemental valence, and photoluminescence properties were characterized by using scanning electron microscope, X-ray diffractometer, X-ray photoelectron spectrometer and photoluminescence analyser, respectively. Results show that preparing conditions and annealing temperatures have significant effects on the crystalline structure and photoluminescence performance. The sample TmZNT-Org prepared in formamide + glycerol organic solution is mainly monoclinic phase and the sample TmZNT-Aq prepared in aqueous solution is mainly tetragonal phase. The sample TmZNT-Org had the strongest photoluminescence peak when annealed at 800 °C, whereas both TmZNT-Aq samples annealed at 600 °C and 800 °C had the strongest photoluminescence peak. The monoclinic phase was conductive to the emission at 454 nm while the tetragonal phase was conductive to the emission at 460 nm.

Preparation and photoluminescence properties of Sm3+-doped ZrO2 nanotube arrays

Zr–Sm (3 at.% Sm) alloy was prepared through a powder metallurgical method. Sm3+-doped ZrO2 nanotube arrays have been achieved directly by anodizing the Zr–Sm alloy. The effects of electrolyte and annealing temperature on the morphologies and structures of the nanotube arrays were studied. The photoluminescence properties of Sm3+-doped ZrO2 nanotube arrays prepared in aqueous solution and formamide + glycerol solution were studied in detail as well. Results show that tetragonal ZrO2 promoted the photoluminescence efficiency of this system. Under excitation at 407 nm, the sample prepared in aqueous solution annealed at 600 °C displayed the strongest emission peak at 571 nm, corresponding to the 4G5/2 → 6H5/2 samarium transition.

Compressive mechanical property of porous magnesium composites reinforced by carbon nanotubes

Porous magnesium/carbon nanotube (Mg/CNT) composites with various CNT concentrations (0.05 and 1 wt%) and overall porosities (20, 30, and 40 %) were synthesized by a powder metallurgical method and characterized to study their microstructure and yield strengths. The introduction of pores leads to the reduction of material strength. Thus, it is attractive to add reinforcement phase to produce porous composites and improve yield strength. The porous Mg/CNT composites with low overall porosity have smaller average pore size than the porous Mg/CNT composites with high overall porosity. The compression testing results showed that the average yield strength is about one to four times of the yield strength of sand-cast Mg. Yield strength of porous Mg–0.05 wt%CNT composites is not significantly different from that of porous Mg–1 wt%CNT composites, when both composites have the same overall porosity. The average yield strength along the in-plane direction is larger than that along the normal direction for each type of porous Mg/CNT composite. The Gibson and Ashby model was used to estimate yield strength and the results show that the theoretical estimations of yield strength agree well with the experimental yield strength values for the porous composites with high overall porosity (i.e., 30 or 40 %), while the estimations are lower than the experimental data for the porous composites with low overall porosity (i.e., 20 %).

Powder Metallurgical Techniques for Fabrication of Biomaterials

Different powder metallurgical techniques have been intensively studied as candidates of methods suitable for fabrication of metallic biomaterials intended for orthopedic applications. The main advantage of powder metallurgical products is that they contain porosity which compromises their mechanical properties closer to those of human bone and allows transport of bodily fluid and growth of ne tissue through the implant. This enhances the healing process; moreover, the pores may be also impregnated by drugs or growth factors, which are eluted during healing and support the healing process. Recently, Ti-based and Mg-based materials have been the most investigated metallic biomaterials; therefore, the powder metallurgical methods are usually studied on those materials. In this paper, the most investigated methods will be summarized and briefly described.

Influence of Mo2C and TaC additions on the microstructure and mechanical properties of Ti(C, N)-based cermets

In this paper, the effects of Mo2C and TaC additions on the microstructure and mechanical properties of Ti(C, N)-based cermets prepared through the powder metallurgical method were investigated by scanning electron microscopy, X-ray diffraction and mechanical properties tests. The results show that the microstructure of cermets with core/rim structure have a trend to become finer with increasing Mo2C and TaC content. The addition of Mo2C and TaC improve the mechanical properties of Ti(C, N)-based cermets. The cermets with 5wt% Mo2C and 5wt% TaC addition demonstrate excellent hardness and fracture toughness values (HRA: 91.4; KIC: 13.5MPam1/2).