Mechanical Alloying Duration Research Articles

Development of Mechanically Alloyed and Sintered W-1 wt.% Ni Matrix Composites Reinforced with TiB<sub>2</sub>

Due to improve the physical and mechanical properties of Ni activated W compacts, TiB2 was added to the W-Ni matrix as reinforcing agent. W-Ni matrix composites were fabricated by using a combined method of mechanical alloying (MA), cold pressing and activated sintering. The amount of activated sintering aid (Ni) was kept constant as 1 wt.%. The effects of TiB2 content and mechanical alloying duration on the physical, microstructural and mechanical properties of activated sintered W-Ni compacts were investigated. The results showed that TiB2 particles have a significant effect on the density and microhardness values of the sintered samples. After MA and sintering, formation of W2B and NiTi intermetallic compounds were observed because of the decomposition of TiB2. The relative density value of 91.21 % and microhardness value of 4.08±0.28 GPa of W-1 wt.% Ni samples respectively increased to 94.88 % and 5.64±0.28 GPa with the addition of 2 wt.% TiB2.

Influences of metallic Co and mechanical alloying on the microstructural and mechanical properties of TiB2 ceramics prepared via pressureless sintering

Abstract This study reports the influences of metallic cobalt (Co) and mechanical alloying (MA) on the microstructural and mechanical properties of TiB2 ceramics prepared by using a combined method of cold pressing and sintering. The effects of Co addition (0, 5, 10 and 20 wt.%) and mechanical alloying duration (0, 3, 6 and 9 h) on the properties of TiB2 ceramics were investigated. MA experiments were carried out in a Spex™ 8000D Mixer/Mill and milled powders were subsequently compacted to cylindrical preforms by uniaxial pressing at 400 MPa. The green compacts were sintered in a controlled atmosphere at 1550 °C for 1 h. Phase and microstructural characterizations of the mechanically alloyed (MA’d) and sintered samples were performed by X-ray diffractometer (XRD), optical microscope (OM) and scanning electron microscope (SEM). Density measurements were conducted using Archimedes method. Vickers hardness, elastic modulus and fracture toughness of the sintered samples were measured using Indentation technique.

Aluminum diboride synthesis from elemental powders by mechanical alloying and annealing

In this study, AlB2 powders were synthesized by using a combined method of mechanical alloying (MA) and annealing of elemental aluminum (Al) and boron (B) powders. Milling was performed in a planetary ball-mill (Fritsch™ Pulverisette 7 Premium Line) up to 15 h under argon (Ar) atmosphere. Annealing process was carried out in a tube furnace at 650 °C for 6 h under Ar atmosphere. The effects of MA durations on the annealing process and AlB2 formation were investigated. The conversion of Al and B powders to AlB2 starts after only MA for 3 h or after MA for 1 h and subsequent annealing. A slight formation of AlB12 occurs at 242 °C for as-blended powders and it shifts to about 272 °C for MA’d powders. Al–B powder blends MA’d for 9 h and annealed have AlB2 particles in size between 35 and 75 nm in the presence of Al13Fe4, Fe3B and Fe2B contaminations.

Martensitic transformation of Ti50Ni30Cu20 alloy prepared by powder metallurgy

Phase transformation behavior of Ti50Ni30Cu20 shape memory alloys prepared by powder metallurgy is analyzed with respect to the duration of mechanical alloying. The processed blends were studied by differential scanning calorimetry and room temperature X-ray diffraction. The martensitic transformations evidenced by thermal scans are discussed in correlation with the relative phase content obtained from the refinement of the X-ray diffraction patterns.

Spark plasma sintering consolidation of nanostructured TiC prepared by mechanical alloying

Spark plasma sintering technique was used for the consolidation of nanostructured titanium carbide synthesized by mechanical alloying in order to avoid any important grain growth of the compact materials. The TiC phase was obtained after about 2 h of mechanical alloying. Towards the end of the milling process (20 h), the nanocrystalline powders reached a critical size value of less than 5 nm. Some physical and mechanical properties of the consolidated carbide were reported as a function of the starting grain size powders obtained after different mechanical alloying durations. The crystalline grain size of the bulk samples was found to be increased to a maximum of 120 nm and 91 nm for carbides mechanically alloyed for 2 h and 20 h respectively. The Vickers hardness showed to be improved to about 2700 Hv for a maximum density of 95.1% of the bulk material.

Hydrogen sorption characteristics of the composites 90 wt.% Mg (MgH2)–10 wt.% V0.855Ti0.095Fe0.05

The hydrogen absorption–desorption characteristics of composites containing 90 wt.% Mg or MgH2 and 10 wt.% of the intermetallic compound V0.855Ti0.095Fe0.05 obtained by mechanical alloying for 1 and 5 h in an inert medium were investigated. Absorption measurements were performed under a hydrogen pressure P = 1 MPa at temperatures of 623, 573, 523, and 473 K. Dehydriding was studied at 623 and 573 K and a pressure of 0.15 MPa. It was established that the presence of the additive improved significantly the hydriding kinetics of magnesium while the effect of the duration of mechanical alloying was less pronounced. Due to the small difference in specific surface areas and crystallite sizes, both composites investigated showed no substantial difference in behavior during absorption and desorption of hydrogen. The best absorption–desorption properties were found with the composite 90 wt.% Mg–10 wt.% V0.855Ti0.095Fe0.05 mechanically activated for 5 h.

Powder Metallurgical Fabrication and Characterization of Nanostructured Porous NiTi Shape-Memory Alloy

Production of NiTi alloy from elemental powders was conducted by mechanical alloying (MA) and sintering of the raw materials. Effects of milling time and milling speed (RPM) on crystallite size, lattice strain, and XRD peak intensities were investigated by X-ray analysis of the alloy. Powder compaction and sintering time and temperature effects on pore percentage of the as-mixed and the mechanically alloyed samples were empirically evaluated. The crystallite size of the mechanically alloyed Ni50Ti50 samples decreased with MA duration and with the milling speed. Depending on the crystal structure of the raw materials, the lattice strain increases with the milling duration. Metallographic studies proved the existence of martensitic B19′ after sintering of both the as-mixed and the mechanically alloyed samples. Its amount was, however, greater for the former. Sintering lowered the porosity of the samples; no matter what powder (as-mixed or mechanically alloyed) was used. The porosity was greater, however, for the MA powders. This difference seemed to be due to the sharper liquid phase sintering effect of the as-mixed samples.

Production and characterization of in situ Fe–Fe 3C composite produced by mechanical alloying

In this study, mechanical alloying (MA) of elemental iron powders containing 1 wt% carbon was carried out under Ar atmosphere by using a high-energy ball mill for various milling time. In order to compare and determine the effect of MA on properties the same amount of powders were mixed by a conventional mixer up to 5 h. Particle size, shape and compressibility of the alloyed powders depending on the milling time were characterized. Powders were compacted at 1000 MPa to produce standard transverse rupture strength specimens. Specimens were then sintered at various temperatures for 2 h under Ar atmosphere in a tube furnace. Optical and SEM studies were conducted in order to determine the effect of temperature and MA durations on the degree Fe 3C transformation on sintered specimen. Transverse rupture strength and hardness tests were carried out to find the mechanical properties of specimens. The results showed that the hardness, transverse rupture strength and microstructure of sintered compact specimens were affected by mechanical alloying time and sintering temperature.

Investigation of the effects of textural properties on marble cutting with diamond wire

In this study, x wt% LaB6 (x = 0, 2, 5 and 10) particulate-reinforced eutectic Al-12.6 wt% Si powders and composites were prepared from commercial Al, Si and LaB6 starting materials via powder metallurgy methods. Mechanical alloying (MA) was conducted on the blended powders using a high-energy ball mill (at 1060 cycles/min) for 2, 4 and 8 h. Mechanically alloyed (MA'd) powders were subjected to cold pressing (CP, under 450 MPa) and spark plasma sintering (at 450 °C for 180 s) processes. Powder particle morphologies changed from flaky to semi-equiaxial shape after MA duration of 4 h. Calculations performed through the XRD patterns of Al phase revealed that the average crystallite size increased and the average lattice strain decreased with increasing MA duration and LaB6 content. Spark plasma sintered (SPS'd) samples were examined in terms of composition, microstructure, densification and mechanical properties (hardness, yield strength, compressive strength and wear volume loss). Studies revealed that 4 h was the optimal MA duration and 10 wt% was the optimal reinforcement content for the LaB6particulate-reinforcedAl-12.6 wt% Si composites with respect to their mechanical properties. Al-12.6 wt% Si-10 wt% LaB6 sample had the highest hardness (1.72 ± 0.12 GPa), yield strength (373 MPa), compressive strength (578 MPa) and lowest wear rate (0.001 mm3/Nm) values among all SPS'd samples.

Production and characterization of in situ Al4C3 reinforced aluminum-based composite produced by mechanical alloying technique

In this study, aluminum powders were mixed with carbon black and mechanically alloyed in a high-energy ball mill for up to 30 h under argon atmosphere. XRD results showed that no Al4C3 formed during the mechanical alloying (MA) process. Mechanically alloyed powders were then compacted at 650 MPa pressure to produce transverse rupture blanks. These blanks were then sintered at 600 and 650 °C for 5, 10 and 20 h under argon atmosphere. X-Ray diffraction analysis of the sintered blocks showed the presence of Al4C3 phase. Increasing MA processing time, sintering temperature and duration, resulted in an increase in the amount of Al4C3 phase. XRD and SEM analysis showed that the most Al4C3 transformation occurred in the blank, which was mechanically alloyed for 30 h and sintered for 20 h at 650 °C. The highest hardness value (347 Hv) was obtained in this blank. Transverse rupture strengths of the sintered blanks were between 6.32 and 234.16 MPa. The highest value was obtained for the blank, which was mechanically alloyed for 15 h and sintered for 20 h at 650 °C.

Investigation of the machinability behaviour of Al 4C 3 reinforced Al-based composite produced by mechanical alloying technique

In this study, by the technique of mechanical alloying (MA), aluminium-based composite reinforced contained various amounts of Al 4C 3 particles, depending on MA time, were produced. The machinability of metal-matrix composites (MMCs) was characterised by the investigation of chip formation, cutting forces and surface roughness. XRD, SEM and mechanical properties of the block samples produced by powder metallurgy technique were investigated. It was found that increasing the duration of mechanical alloying resulted in the formation higher amounts of Al 3C 4 particles which therefore raised the hardness, but on the contrary decreased the transverse rupture strength of the samples. During the machining of MMCs, elemental and arc chips formation were observed. High volume fraction of Al 4C 3 in the matrix decreased formation of built-up edge (BUE) and surface roughness at high cutting speeds. Furthermore, it was concluded that the effect of Al 4C 3 on the crack formation in shear plane, reduced the cutting force, shortened the chip contact length and the chip segment thickness.

Enhanced mechanical properties of an Al based metal matrix composite prepared using mechanical alloying

An Al–4.5wt.%Cu–10vol.%SiCp composite has been prepared using a mechanical alloying technique. The structural evolution of the mechanically alloyed powder mixture was monitored using X-ray diffractometry while its thermal behaviour was determined using differential scanning calorimetry. The results showed that both the 0.2% yield and the ultimate tensile stresses increased with the duration of mechanical alloying. This increase is associated with the homogeneous distribution and refinement of the SiC particulates, the formation of oxides and the decreased grain size. The thermal fatigue behaviour of the composite has also been investigated using thermal cycling between −15 and 150°C. The tensile tests on the thermal cycled specimens were carried out to study the influence of thermal cycling on the mechanical properties of the material. It was found that although the 0.2% yield and the ultimate tensile stresses had improved, cracks had been observed in the matrix material. These cracks may have led to the final failure of the test specimens.

Thermodynamic properties of mechanically alloyed nickel and aluminum powders

Thermodynamic properties of mechanically alloyed Ni and Al powders were analyzed using differential scanning calorimetric after different durations of mechanical alloying. Results show an increase in stored enthalpy in the alloyed powders with increase in mechanical alloying duration. The temperatures at which Ni 3Al intermetallic compound formed were lowered when milling time was prolonged. After 300 minutes of mechanical alloying, a transition reaction from disordered fcc to ordered Ll 2 of intermetallic compound was observed. X-ray diffraction patterns also confirmed the formation of Ni 3Al intermetallic compound after that time. Further mechanical alloying was found to lower the transition temperature which was related to the increase in stored energy.