Structure and thermal conductivity of powder injection molded AlN ceramic

AlN powders doped with Y₂O₃ (5 wt.%) were compacted by employing powder injection molding (PIM) technique. The binder consisted of paraffin wax (PW, 60 wt.%), polypropylene (PP, 35 wt.%) and stearic acid (SA, 5 wt.%). The feedstock was prepared with a solid loading of 62 vol.%. The binder was removed through debinding process in two steps, solvent debinding followed by thermal debinding. At last, the debound samples were sintered in flowing nitrogen gas at atmospheric pressure. The result reveals that thermal debinding atmosphere has significant effect on the thermal conductivity and structure of AlN ceramics. The thermal conductivity of injection molded AlN ceramics thermal debound in flowing nitrogen gas is 231 W m^?1 K^?1.     

Microstructure and tensile strength of PM304 composite

PM304 composite comprising NiCr (80/20) matrix (60 wt.%) combined with Cr₂O₃ (20 wt.%), Ag (10 wt.%) and eutectic BaF₂/CaF₂ (10 wt.%) as solid self-lubricants additives has been successfully prepared by mechanical alloying and powder metallurgy. The sintered PM304 samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDXS). The density of PM304 composite sintered at 1100 °C was 7.3 g/cm³, and the mean tensile strength 47 MPa. The size of Cr₂O₃, BaF₂/CaF₂ particles was less than 1 μm, and that of Ag particles below 5 μm. Fracture morphology indicates that the fracture of PM304 is mainly along Ni80Cr20 grains.     

Densification behavior,mechanical properties and thermal shock resistance of tungsten alloys fabricated at low temperature

The low-temperature shrinkage of tungsten was greatly accelerated by the addition of trace Nb and Ni, and the addition of trace Nb and Ni also significantly promoted the final sintering density. The 99.1% of theory density for W–0.1 wt.%Nb–0.1 wt.%Ni material sintered at 1600 °C was obviously greater than 93.7% of theory density for W material sintered at 2000 °C. Ball milling treatment played an important role in promoting the sintering densification of W–0.1 wt.%Nb–0.1 wt.%Ni powder, and the powder milled for 10 h (W10) could be sintered to near full density (99.4% of theory density) at 1600 °C. The ball milling for 15 h has no effect in improving the sintering density, but it induced rapid growth of tungsten grains. The microhardness and tensile strength of the sintered tungsten alloys were highly dependent on its sintering density and grain size. Improving the sintering density while controlling the grain growth could effectively promote the microhardness and tensile strength. Furthermore, the improvement of thermal shock resistance of the W10 alloy was due to good microstructure and the increase in the tensile strength.     

The effect of Mg add on morphology and mechanical properties of Al–xMg/10Al2O3 nanocomposite produced by mechanical alloying

Effect of Mg content on microstructure and mechanical properties of Al–xMg/10 wt.%Al₂O₃ (x = 0, 5, 10 and 15 wt.%) powder mixtures during milling was investigated. The results show that for the binary Al–Mg matrix, the predominant phase was an Al–Mg solid solution. With the increment of Mg to 15 wt.% the crystallite sizes of 20 h milled powders diminish from 44 to 26 nm and lattice strains increased from 0.22% to 0.32% caused by Mg atomic penetration into the substitution sites of the Al lattice. With up to 15 wt.% Mg (for 20 h milled composites) microhardness increases from 120 to 230 HV caused by the increment of the Mg concentration and dislocation density as well as the decrease of the crystallite size.     

Fabrication and properties of mechanically alloyed and Ni activated sintered W matrix composites reinforced with Y2O3 and TiB2 particles

Microstructural and physical properties of W–1 wt.% Ni matrix composites reinforced with Y₂O₃ and TiB₂ particles produced via mechanical alloying and sintering at 1400 °C for 1 h under Ar, H₂ gas flowing conditions were investigated. XRD patterns of the sintered samples revealed the presence of W, Ni and TiB₂ phases, whereas W₂B and NiTi phases were detected in the samples containing 4 wt.% and 5 wt.% TiB₂. Relative density value of W–1 wt.% Ni sample was measured as 97%, which decreased to 95.4% with the addition of 0.5 wt.% Y₂O₃. Relative density values varied between 95.4% and 97.3% for the sintered samples containing varying TiB₂ between 1 wt.% and 5 wt.%. Average W grain size in the sintered samples decreased with the addition of Y₂O₃ and TiB₂ particles, from 5.38 μm in the W–1 wt.% Ni sample to 0.8 μm in the W–1 wt.% Ni sample containing 0.5 wt.% Y₂O₃ and 5 wt.% TiB₂ particles. Vickers microhardness values varied between 4.53 GPa and 8.54 GPa. The sample with the composition of W–1 wt.% Ni/0.5 wt.% Y₂O₃ and 5 wt.% TiB₂ had a relative density value of about 95.7% and hardness value of 8.54 GPa after sintering at 1400 °C for 1 h.     

Reliability of mechanical properties of induction sintered iron based powder metal parts

Reliability and safety are important for machine and construction elements. In this study, iron based powder metal parts (3% Cu, 0.5% Graphite and 1% Kenolube lubricant by weight) were sintered at 1200 °C by medium frequency induction sintering mechanism (30 KW powered and 30 kHz frequency). Mechanical property values of components were determined according to changing sintering time. Three point bending, % maximum strain, MicroVickers hardness (HV) and Rockwell-B hardness tests were applied. Statistical distribution functions were drawn and ultimate strength, ultimate strain, MicroVickers and Rockwell-B hardness values were determined depending on various reliability. As a result of the experiments, it was concluded that, the hardness of powder metal materials should not be based on MicroVickers hardness.     

An investigation of the effect of SiC particle size on Cu–SiC composites

In this study mechanical properties of copper were enhanced by adding 1 wt.%, 2 wt.%, 3 wt.% and 5 wt.% SiC particles into the matrix. SiC particles of having 1 μm, 5 μm and 30 μm sizes were used as reinforcement. Composite samples were produced by powder metallurgy method and sintering was performed in an open atmospheric furnace at 700 °C for 2 h. Optical and SEM studies showed that the distribution of the reinforced particle was uniform. XRD analysis indicated that the dominant components in the sintered composites were Cu and SiC. Relative density and electrical conductivity of the composites decreased with increasing the amount of SiC and increased with increasing SiC particle size. Hardness of the composites increased with both amount and the particle size of SiC particles. A maximum relative density of 98% and electrical conductivity of 96% IACS were obtained for Cu–1 wt.% SiC with 30 μm particle size.     

Fabrication and characterization of Ni–W solid solution alloys via mechanical alloying and pressureless sintering

Ni–W solid solution alloy powders and sintered compacts were fabricated via mechanically alloying and pressureless sintering of powder batches with the compositions of Ni–xW (x = 20, 30, 40 wt.%). The crystallite size of the powders were between 11 nm and 17 nm, which decreased with increasing W contents, where a microhardness value of 6.88 GPa for the Ni powders MM’d for 48 h increased to 9.37 GPa for the Ni40W powders MA’d for 48 h. The MM’d/MA’d powders were sintered at 1300 °C for 1 h under Ar and H₂ gas flowing conditions. X-ray diffraction (XRD) patterns of the sintered Ni, Ni20W and Ni30W samples revealed the presence of only the solid solution phase, whereas the presence of elemental W and Ni₄W intermetallic phase were observed in the XRD patterns of the sintered Ni40W sample. Among all sintered samples, the sintered Ni sample had the highest relative density value of 96.36% and the lowest microhardness value of 1.59 GPa. The relative densities of the sintered samples decreased with increasing W amounts, contrary to microhardness values which increased with W contents. Moreover, microstructural characterizations via scanning electron microscope and electron backscatter diffraction, room temperature compression tests and sliding wear experiments were conducted in order to reveal the effects of W contents on the properties of the sintered Ni–W alloys.     

Metal injection molding of pure molybdenum

In this work the processing steps for producing molybdenum parts by means of metal injection molding technique, including milling, mixing, debinding and sintering, were investigated in detail. Different feedstocks were prepared from received and milled molybdenum powder and a thermoplastic binder based on paraffin wax. The feedstock including 50% by volume of milled molybdenum powder had better rheological property and was injected successfully at low pressure. The molded specimens were debinded by two different processes, direct thermal debinding and solvent–thermal debinding. The content of carbon and oxygen were respectively less than 0.060% and 0.0042% after the parts were sintered under hydrogen atmosphere. The parts sintered at 1850 °C for 120 min exhibited a highest density of 9.70 g/cm³,meanwhile the tensile strength and hardness was 229 MPa and 193 HV10, respectively.     

Improved mechanical properties of recycled linear low-density polyethylene composites filled with date palm wood powder

Recycled linear low-density polyethylene (RLLDPE) was blended with date palm wood powder to prepare composites in which the concentration of the filler ranged from 10 to 70 wt.%. The cross-linking of composites was performed in some selected cases. The Young’s modulus of the composites significantly increased as the filler content increased over the entire concentration range. A maximum value of 1989 MPa was observed for the composite filled with 70 wt.% filler, which was approximately 6.5 times higher than that observed for neat RLLDPE. The presence of filler increased the flexural strength from 11.4 MPa for unmodified RLLDPE to 17 MPa for the composite containing 70 wt.% filler. The Young’s modulus and stress at break measured at 50 °C decreased significantly compared with those values measured at 25 °C. The ratio between the stress at break at 25 °C versus 50 °C (σ₂₅/σ₅₀) was between 2.7 and 3.8, whereas the ratio of Young’s modulus of E₂₅/E₅₀ was between 1.6 and 2.6.     

Effect of 10Ce-TZP/Al2O3 nanocomposite particle amount and sintering temperature on the microstructure and mechanical properties of Al/(10Ce-TZP/Al2O3) nanocomposites

A zirconia/alumina nanocomposite stabilized with cerium oxide (Ce-TZP/Al₂O₃ nanocomposite) can be a good substitute as reinforcement in metal matrix composites. In the present study, the effect of the amount of 10Ce-TZP/Al₂O₃ particles on the microstructure and properties of Al/(10Ce-TZP/Al₂O₃) nanocomposites was investigated. For this purpose, aluminum powders with average size of 30 μm were ball-milled with 10Ce-TZP/Al₂O₃ nanocomposite powders (synthesized by aqueous combustion) in varying amounts of 1, 3, 5, 7, and 10 wt.%. Cylindrical-shape samples were prepared by pressing the powders at 600 MPa for 60 min while heating at 400–450 °C. The specimens were then characterized by scanning and transmission electron microscopy (SEM and TEM) in addition to different physical and mechanical testing methods in order to establish the optimal processing conditions. The highest compression strength was obtained in the composite with 7 wt.% (10Ce-TZP/Al₂O₃) sintered at 450 °C.     

Preparation of a–b plane oriented Nb-doped Bi4Ti3O12 ceramics by magnetic alignment via gelcasting

Highly a–b plane grain-oriented Nb-doped Bi₄Ti₃O₁₂ ceramics (Bi₄Ti_2.96Nb_0.04O₁₂, BINT) were successfully prepared by magnetic alignment (MA) via gelcasting technique using only conventional solid-state-synthesized starting powder. The micro-size BINT particles with irregular shape were aligned in slurry by strong magnetic force and then in situ locked by polymerization via gelcasting technique in 30 min in a 10 T magnetic field. Highly a–b plane orientation parallel to the magnetic field direction (//B) was obviously observed in the green compact (f_(200)/(020) = 0.41) and sintered sample (f_(200)/(020) = 0.67). The sintered sample contained plate-like grains and reached 97% theoretical density. Compared to the controlled sample without magnetic alignment, the magnetically aligned sample shows enhanced dielectric constant in //B direction (160 versus 120 at room temperature and 350 versus 250 at 580 °C). This method, using typical gelcasting technique in a strong magnetic field, readily applicable to prepare other ceramics and is expected to facilitate the mass preparation of large and dense grain-oriented ceramic components.     

Effect of impact force on Ti–10Mo alloy powder compaction by high velocity compaction technique

Ti–10Mo alloy powder were compressed by high velocity compaction (HVC) in a cylinderical form of height/diameter (h/d) in die 0.56 (sample A) and 0.8 (sample B). Compactions were conducted to determine the effect of impact force per unit area of powder filled in die for densification and mechanical properties of Ti–10Mo samples. The micro structural characterization of samples were performed by scanning electron microscope (SEM). The mechanical properties of the compressed samples such as Vickers hardness, bending strength, and tensile strength were measured. Experimental results showed that the density and mechanical properties of sample A and sample B increased gradually with an increase in impact force and decreased with an increase in height/diameter ratio. The relative green density for sample A reached up to 90.86% at impact force per unit area 1615 N mm⁻². For sample B, it reached 79.71% at impact force per unit area 1131 N mm⁻². The sintered sample A exhibited a maximum relative density of 99.14%, Vickers hardness of 387 HV, bending strength of 2090.72 MPa, and tensile strength of 749.82 MPa. Sample B revealed a maximum relative sintered density of 97.73%, Vickers hardness of 376 HV, bending strength 1259.94 MPa and tensile strength 450.25 MPa. The spring back of the samples decreased with an increase in impact force.     

The effects of annealing temperature on the in-field Jc and surface pinning in silicone oil doped MgB2 bulks and wires

The effects of sintering temperature on the lattice parameters, full width at half maximum (FWHM), strain, critical temperature (T_c), critical current density (J_c), irreversibility field (H_irr), upper critical field (H_c2), and resistivity (ρ) of 10 wt.% silicone oil doped MgB₂ bulk and wire samples are investigated in state of the art by this article. The a-lattice parameter of the silicone oil doped samples which were sintered at different temperatures was drastically reduced from 3.0864 Å to 3.0745 Å, compared to the un-doped samples, which indicates the substitution of the carbon (C) into the boron sites. It was found that sintered samples at the low temperature of 600 °C shows more lattice distortion by more C-substitution and higher strain, lower T_c, higher impurity scattering, and enhancement of both magnetic J_c and H_c2, compared to those sintered samples at high temperatures. The flux pinning mechanism has been analyzed based on the extended normalized pinning force density f_p = F_p/F_p,max scaled with b = B/B_max. Results show that surface pinning is the dominant pinning mechanism for the doped sample sintered at the low temperature of 600 °C, while point pinning is dominant for the un-doped sample. The powder in tube (PIT) MgB₂ wire was also fabricated by using of this liquid doping and found that both transport J_c and n-factor increased which proves this cheap and abundant silicone oil doping can be a good candidate for industrial application.     

Dopant influence on BST ferroelectric solid solutions family

Solid solutions of the Ba_1−xSr_xTiO₃ (BST) type are very attractive for applications in information technology, but also in microwaves for such electrically controlled devices as phase shifters, tunable filters, steerable antennas, varactors, etc. A family of solid solutions with x = 25, 50, 75, 90% was prepared by standard powder technology-solid state reaction and sintered at 1230 °C and 1260 °C. Dielectric permittivity and loss at low (1 kHz) and high frequency (1 ÷ 2 GHz) were measured on a large temperature range − 200 °C ÷ + 200 °C. The influence of Sr content and of 1 wt.% MgO and 1 wt.% MnO₂ doping on the complex dielectric constant was studied. The dielectric permittivity at high frequencies and room temperature considerably decreases with the increase of Sr content. Similarly, low frequency measurements showed a severe and almost linear decrease of the Curie Point with the increase of Sr fraction. At low Sr content, the measured ceramic densities slowly decrease with Sr fraction and represent about 92% of the X-ray density ρ(g/cm³) ≈ 5.99–0.99·x. At x = 90% Sr concentration, very low-density ceramics were obtained with both sintering temperatures.     

Preparation of PMN–PT–BT/Ag nanocomposites by surface modification with MgO sol

Nanocomposites of 0.96(0.91Pb(Mg_1/3Nb_2/3)O₃–0.09PbTiO₃)–0.04BaTiO₃ (PBT) with Ag were prepared via synthesis of low-temperature-sinterable PBT/Ag composite powder and its surface modification with a MgO sol. Dielectric properties and modulus of rupture were investigated as a function of the amount of the MgO sol at sintering temperature in the range from 850 to 1000 °C. The MgO sol seemed to suppress the diffusion and migration of Ag during the heat treatment to give rise to the homogeneous microstructure with 300–80 nm of Ag particles in about 3.5–2.5 μm grains. The proper amount of the MgO sol seemed to be 0.5–1.0 wt.% for the PBT powder with 3.0 mol% Ag. The PBT/Ag nanocomposites showed density >99% T.D., ɛ_rt of 18,000–20,000, tan δ of 1–0.5%, specific resistivity of 10¹² Ω cm, and MOR of 125–145 MPa.     

Preparation of YAG gel coated ZrB2–SiC composite prepared by gelcasting and pressureless sintering

In this paper, gelcasting and pressureless sintering of YAG gel coated ZrB₂–SiC (YZS) composite were conducted. YAG gel coated ZrB₂–SiC (YZS) suspension was firstly prepared through sol–gel route. Poly (acrylic acid) was used as dispersant. YZS suspension had the lowest viscosity when using 0.6 wt.% PAA as dispersant. Gelcasting was conducted based on AM–MBAM system. The gelcast YZS sample was then pressureless sintered to about 97% density. During sintering, YAG promoted the densification process from solid state sintering to liquid phase sintering. The average grain sizes of ZrB₂ and SiC in the YZS composite were 3.8 and 1.3 μm, respectively. The flexural strength, fracture toughness and microhardness were 375 ± 37 MPa, 4.13 ± 0.45 MPa m^1/2 and 14.1 ± 0.5 GPa, respectively.     

High velocity compaction of 0.9Al2O3/Cu composite powder

The 0.9Al₂O₃/Cu composite powder was compacted by high velocity compaction (HVC) technique and the effects of sintering temperature on density and mechanical properties such as tensile strength and hardness were studied. The results showed that with an increase in impact velocity the green density of the compacts significantly increased. At impact velocity of 9.40 m s⁻¹, the maximum green density of the compacts reached up to 8.460 g/cm³ (RD 96.8%). The green compacts were then sintered at different temperatures and it was found that with the increase in sintering temperature the sintered density and the mechanical properties also increased. At sintering temperature of 1080 °C, the compacts obtained the maximum relative sintered density of 98%, a tensile strength of 346 MPa and hardness of 71.1 HRB. Additionally with the increase in sintering temperature, the shrinkage along both axial and radial direction increased. The electrical conductivity of the samples was measured as 71% IACS.     

Aluminum-free glass-ionomer bone cements with enhanced bioactivity and biodegradability

Al-free glasses of general composition 0.340SiO₂:0.300ZnO:(0.250-a-b)CaO:aSrO:bMgO:0.050Na₂O:0.060P₂O₅ (a, b = 0.000 or 0.125) were synthesized by melt quenching and their ability to form glass-ionomer cements was evaluated using poly(acrylic acid) and water. We evaluated the influence of the poly(acrylic acid) molecular weight and glass particle size in the cement mechanical performance. Higher compressive strength (25 ± 5 MPa) and higher compressive elastic modulus (492 ± 17 MPa) were achieved with a poly(acrylic acid) of 50 kDa and glass particle sizes between 63 and 125 μm. Cements prepared with glass formulation a = 0.125 and b = 0.000 were analyzed after immersion in simulated body fluid; they presented a surface morphology consistent with a calcium phosphate coating and a Ca/P ratio of 1.55 (similar to calcium-deficient hydroxyapatite). Addition of starch to the cement formulation induced partial degradability after 8 weeks of immersion in phosphate buffer saline containing α-amylase. Micro-computed tomography analysis revealed that the inclusion of starch increased the cement porosity from 35% to 42%. We were able to produce partially degradable Al-free glass-ionomer bone cements with mechanical performance, bioactivity and biodegradability suitable to be applied on non-load bearing sites and with the appropriate physical characteristics for osteointegration upon partial degradation. Zn release studies (concentrations between 413 μM and 887 μM) evidenced the necessity to tune the cement formulations to reduce the Zn concentration in the surrounding environment.     

Characterization,sintering and dielectric properties of nanocrystalline barium titanate synthesized through a modified combustion process

Nanocrystalline barium titanate has been synthesized through a modified combustion process in a single step for the first time. The as-prepared barium titanate powder is cubic perovskite with lattice constant a = 4.018 Å. The phase purity of the nanopowder was examined using thermo gravimetric analysis, differential thermal analysis and Fourier transform infrared spectroscopy. Transmission electron microscopic investigations have shown that the particle size of the as-prepared powder is in the range 20–40 nm. The agglomerate size distribution of the as-prepared powder was studied using atomic force microscopy. The nanoparticles of barium titanate were sintered to 97% of the theoretical density at a temperature of 1350 °C for 3 h. The microstructure of the sintered surface was examined using scanning electron microscopy. The dielectric constant and loss factor of the sintered pellets at 1 MHz measured at room temperature were 1223 and 3.5 × 10^? 3 respectively.