Mechanism of low-temperature theta-CuGa2 phase formation in Cu-Ga alloys by mechanical alloying

The mechanism on the formation of the theta-CuGa2 phase in binary Cu-Ga alloys has been investigated through mechanical alloying (MA) of blended elemental powders by varying process variables such as milling time and milling temperature. The particle size distribution was very broad at the beginning of milling but became narrower as the milling time increased and steady-state equilibrium was reached. The average powder particle size reached a peak value of 270 mum at 30 min of milling and then continued to decrease gradually to 6 mum on milling for 20 h. Formation of the theta-CuGa2 phase started to occur even after milling for 2 min and was completed after 1 h of milling. Melting of Ga was noted in the early stages of milling, probably due to the rise in powder temperature. To discount the possibility that the melting of Ga was responsible for the theta-phase formation, milling was conducted at lower temperatures by dripping liquid nitrogen on to the container. The theta-phase still formed, suggesting that its formation was not related to the melting of Ga and that it was formed by a solid-state reaction even at low temperatures. The compositional homogeneity range of the theta-phase was also extended under the MA conditions. Details of the mechanism of phase formation, as observed by x-ray diffraction and scanning electron microscopy methods, are presented

Effect of Magnetic Pulsed Compaction (MPC) on sintering behavior of materials

Soon-Jik Hong, Md. Raihanuzzaman Rumman and Chang Kyu Rhe

Effect of mechanical alloying on the microstructural evolution of a ferritic ODS steel with (Y-Ti-Al-Zr) addition processed by Spark Plasma Sintering (SPS)

The high-energy milling is one of the most extended techniques to produce Oxide dispersion strengthened (ODS) powder steels for nuclear applications. The consequences of the high energy mill process on the final powders can be measured by means of deformation level, size, morphology and alloying degree. In this work, an ODS ferritic steel, Fe-14Cr-5Al-3W-0.4Ti-0.25Y2O3-0.6Zr, was fabricated using two different mechanical alloying (MA) conditions (Mstd and Mact) and subsequently consolidated by Spark Plasma Sintering (SPS). Milling conditions were set to evidence the effectivity of milling by changing the revolutions per minute (rpm) and dwell milling time. Differences on the particle size distribution as well as on the stored plastic deformation were observed, determining the consolidation ability of the material and the achieved microstructure. Since recrystallization depends on the plastic deformation degree, the composition of each particle and the promoted oxide dispersion, a dual grain size distribution was attained after SPS consolidation. Mact showed the highest areas of ultrafine regions when the material is consolidated at 1100 degrees C. Microhardness and small punch tests were used to evaluate the material under room temperature and up to 500 degrees C. The produced materials have attained remarkable mechanical properties under high temperature conditions.Authors want to acknowledge Ferro-Ness project and Ferro- Genesys project funded by MINECO under National I + D + I program MAT2016-80875-C3-3-R and MAT2013-47460-C5-5-P

Low Temperature Phase Formation In Mechanically Alloyed Cu-Ga Powders

The mechanism of formation of the θ-CuGa2 phase in binary Cu-Ga alloys has been investigated through MA of blended elemental powders by varying process variables such as milling time and milling temperature. The phase formation started even after milling for 2 min and was complete after 1 h of milling. Melting of Ga was noted in the early stages of milling, probably due to the rise in powder temperature. To discount the possibility that melting of Ga was responsible for the θ-phase formation, milling was conducted at lower temperatures by dripping liquid nitrogen on to the container. The θ-phase still formed, suggesting that its formation was not related to melting of Ga and that it had formed by a solid-state reaction even at low temperatures. The compositional homogeneity range of the θ-phase was also extended under MA conditions

Mechanical Properties And Fracture Behavior Of An Ultrafine-Grained Al-20 Wt Pct Si Alloy

The effect of powder particle size on the microstructure, mechanical properties, and fracture behavior of Al-20 wt pct Si alloy powders was studied in both the gas-atomized and extruded conditions. The microstructure of the as-atomized powders consisted of fine Si particles and that of the extruded bars showed a homogeneous distribution of fine eutectic Si and primary Si particles embedded in the Al matrix. The grain size of fcc-Al varied from 150 to 600 nm and the size of the eutectic Si and primary Si was about 100 to 200 nm in the extruded bars. The room-temperature tensile strength of the alloy with a powder size \u3c26 μm was 322 MPa, while for the coarser powder (45 to 106 μm), it was 230 MPa. The tensile strength of the extruded bar from the fine powder (\u3c26 μm) was also higher than that of the Al-20 wt pct Si-3 wt pet Fe (powder size: 60 to 120 μm) alloys. With decreasing powder size from 45 to 106 μm to \u3c26 μm, the specific wear of all the alloys decreased significantly at all sliding speeds due to the higher strength achieved by ultrafine-grained constituent phases. The thickness of the deformed layer of the alloy from the coarse powder (10 μm at 3.5 m/s) was larger on the worm surface in comparison to the bars from the fine powders (5 μm at 3.5 m/s), attributed to the lower strength of the bars with coarse powders. © ASM International & TMS-The Minerals Metals and Materials Society 2005

Mechanical Properties And Fracture Mechanism Of Nanostructured Al-20 Wt% Si Alloy

The effect of powder size on the microstructure, mechanical properties and fracture behavior was studied in gas atomized Al-20 wt% Si alloy powders and their extruded bars using SEM, XRD, TEM, tensile testing and wear testing. The microstructure of the extruded bars showed a homogeneous distribution of eutectic Si and primary Si particles embedded in the Al matrix. The grain size of α-Al varied from 150 to 600 nm and the size of the eutectic Si and primary Si in the extruded bars was about 100 - 200 nm. The tensile strength of the Al-20Si (powder size \u3c 26 μm) alloys at room temperature was 322 MPa while for the Al-20Si (powder size: 45-106 μm) it was 230 MPa; this value is higher than that of Al-20Si-3Fe (powder size: 60-120 μm) alloys. With decreasing powder size from 45-106 μm to \u3c 26 nm, the specific wear decreased significantly at all sliding speeds due to the fine nanostructute. The wear resistance was also better than that of the Al-20Si-3Fe alloys. The fracture mechanism of failure in tension testing and wear testing was also studied

Optimization of surface roughness by Taguchi design method

Maintaining good surface quality usually involves additional manufacturing cost or loss of productivity. The Taguchi design is an efficient and effective experimental method in which a response variable can be optimized, given various control and noise factors, using fewer resources than a factorial design. This study included feed rate, spindle speed and depth of cut as control factors, and the noise factors were the operating chamber temperature and the usage of different tool inserts in the same specification. An orthogonal array of L9 (34) was used and the optimal cutting combination was determined by seeking the best surface roughness (response) and signal-to-noise ratio.Rumman Md. Raihanuzzaman, Soon-Jik Hon

Effect Of Clustering On The Mechanical Properties Of Sic Particulate-Reinforced Aluminum Alloy 2024 Metal Matrix Composites

Al 2024-SiC metal matrix composite (MMC) powders produced by centrifugal atomization were hot extruded to investigate the effect of clustering on their mechanical properties. Fracture toughness and tension tests were conducted on specimens reinforced with different volume fractions of SiC. A model was proposed to suggest that the strength of the MMCs could be estimated from the load transfer model approach that takes into consideration the extent of clustering. This model has been successful in predicting the experimentally observed strength and fracture toughness values of the Al 2024-SiC MMCs. On the basis of experimental observations, it is suggested that the strength of particulate-reinforced MMCs may be calculated from the relation: σy = σmVm + σr (Vr-Vc)-σrVc, where σ and V represent the yield strength and volume fraction, respectively, and the subscripts m, r, and c represent the matrix, reinforcement, and clusters, respectively. © 2002 Elsevier Science B.V. All rights reserved

Synthesis Of Nano-Size Hydroxyapatite (Hap) Powders By Mechanical Alloying

Nano hydroxyapatite (Ca 10(PO 4) 6(OH) 2, HAp) powders were synthesized by solid-state reaction of Ca(OH) 2 and P 2O 5 mixtures in a high-energy SPEX 8000 shaker mill, using hardened steel vial and balls. The phase analysis was carried out using X-ray powder diffraction technique. Transformation of Ca(OH) 2 and P 2O 5 mixture to HAp phase was first observed after 1 h of milling. The powder milled for 3 h showed prominently the presence of HAp phase. TEM analysis revealed that as-synthesized HAp powder was in the range of 20-60 nm. Measured quantities of synthesized nano-powders were pressed uniaxially in a steel mold to prepare dense ceramic structures for densification studies. These green structures were subjected to sintering studies at 1300°C for 6 h when the highest sintered density of 3.17 g/cc was achieved