Large Fraction Of Amorphous Phase Research Articles

Microstructure and Wear Properties of HVAF Sprayed Cu-Zr-Al-Ag-Co Amorphous Coatings at Different Spray Temperatures

Wear-resistant Cu-Zr-Al-Ag-Co amorphous coatings were fabricated by high-velocity air-fuel spray technology using (Cu43Zr47Al7Ag3)99.5Co0.5 powder at different temperatures (i.e., 645, 725, and 805 K). The feedstock powders (98.6 wt.% amorphous phase) were produced by a gas atomization method. Thermal properties and microstructure of the powders and the coatings were comparably investigated by differential scanning calorimeter, scanning electron microscope, and transmission electron microscopy techniques. Wear properties were studied by a dry sliding wear tester under the linear reciprocating sliding in a ball-on-plate mode using a GCr15 ball as the counterpart at room temperature in air. A large fraction of amorphous phase (~67.5 wt.%) and crystalline phases (ZrO2, Al2.5Cu0.5Zr, and AlZr3) are found in the coating fabricated at a temperature (725 K) between the glass transition temperature (Tg) and the onset crystallization temperature (Tx). In addition, the coating also exhibits the highest Vickers hardness (554 HV0.1), bonding strength (59.3 MPa), a relatively low porosity (1.65%), and superior wear resistance. The wear mechanism of the coating is primarily abrasive wear and slight adhesive wear.

Evaluation of principal residual stress and its relationship with crystal orientation and mechanical properties of polypropylene films

Evaluation of principal residual stress with X-Ray diffraction for metals has been widely practiced, but not for polymers due to a large fraction of amorphous phase, though it is very important for many engineering applications. Such a method is established for rigid semicrystalline polymer with rubber amorphous which, in the present work, are defined as the polymers with an amorphous rubber phase and a crystal matrix (rigid crystal network) providing its plastic modulus. An equal strain model between crystal and amorphous phases and the Young's modulus contributed by both crystal and amorphous phases, instead of moduli from crystal region, are justified for the stress evaluation for rigid semicrystalline polymers. The principal residual stresses obtained with our approach show a very good correlation with crystal orientation and the anisotropic mechanical properties of the polymer films studied. The established method can be widely used for rigid semicrystalline polymers with rubbery amorphous.

Microstructure and wear behavior of Fe-based amorphous HVOF coatings produced from commercial precursors

Abstract Wear resistant highly amorphous Fe 60 Cr 8 Nb 8 B 24 (at.%) coatings of about 280 μm thickness were prepared through high velocity oxygen fuel (HVOF) thermal spray process onto API 5L X80 steel substrate. Feedstock powders were produced by gas atomization with low purity precursors by modifying AISI 430 stainless steel with additions of niobium (Fe-Nb) and boron (Fe-B). It was found that the coatings were mostly amorphous with some embedded FeNbB and Fe 2 B borides. The formation of a large fraction of amorphous phase was attributed to the high cooling rates of molten droplets combined with a proper powder composition. The average Vickers hardness of the coating (HV 0.3 = 838 ± 23) was about four times higher than that of the API 5L X80 substrate (HV 0.3 = 222 ± 5). The excellent wear resistance of the amorphous coating in the pin-on-disc measurements was attributed to its large fraction of amorphous phase (~ 66%) with reinforcing hard Fe 2 B and FeNbB borides, high Vickers hardness, low oxygen content ( − 5 and 8.5 × 10 − 4 mm 3 ·N − 1 ·m − 1 , respectively). API 5L X80 steel exhibited dominant adhesive wear at low sliding speed and oxidative wear at high sliding speed. HVOF coatings presented oxidative wear regardless of the sliding speed.

In Situ Synthesis and Characterization of Zr-Based Amorphous Composite by Laser Direct Deposition

Zr-based bulk metallic glasses have attracted extensive interest for structural applications due to their excellent glass-forming ability, superior mechanical properties, and unique thermal and corrosion properties. In this study, Zr65Al10Ni10Cu15 amorphous composites with a large fraction of amorphous phase were in situ synthesized by laser direct deposition. X-ray diffraction confirmed the existence of both amorphous and crystalline phases. Laser parameters were optimized in order to increase the fraction of amorphous phase. The microstructure analysis by scanning electron microscopy revealed the deposited structure was composed of periodically repeated amorphous and crystalline phases. Overlapping regions with nanoparticles aggregated were crystallized by laser reheating and remelting processes during subsequent laser scans. Vickers microhardness of the amorphous region showed around 35 pct higher than that of crystalline region. Average hardness obtained by a Rockwell macrohardness tester was very close to the microhardness of the amorphous region. The compression test showed that the fracture strain of Zr65Al10Ni10Cu15 amorphous composites was enhanced from less than 2 pct to as high as 5.7 pct, compared with fully amorphous metallic glass. Differential scanning calorimetry test results further revealed the amorphous structure and glass transition temperature T g was observed to be around 660 K (387 °C). In 3 mol/L NaCl solution, laser direct deposited amorphous composites exhibited distinctly improved corrosion resistance, compared with fully crystallized samples.

Effect of feedstock particle sizes on wear resistance of plasma sprayed Fe-based amorphous coatings

Fe-based amorphous coatings were fabricated by plasma spray technology using Fe43Cr16Mo16C10B5P10 powders with different particle sizes (median size of 33μm, 66μm and 84μm, respectively). XRD results indicated that all of the coatings exhibited a large fraction of amorphous phase. The effect of the feedstock particle sizes on the morphology and microstructure of as-sprayed coatings was investigated by SEM and TEM observations. It was found that the smaller the particle size, the denser the structure with the lower porosity and lesser cracks the coating exhibited. The feedstock particle sizes had a significant effect on the wear resistance of coatings. With a decrease in the particle sizes, the porosity decreased and the cohesion at the intersplat regions and the hardness of the coating improved. Hence, the wear resistance of coating was enhanced. Moreover, the sliding velocity also had different influences on the wear resistance of coatings. Raising the sliding velocity could aggravate the oxidation of the coating and lead to a decrease in the wear resistance. The analysis of the worn surfaces of coatings indicated that the dominating wear mechanism of Fe-based amorphous coatings was fatigue wear accompanied with oxidative wear.

Synthesis and characterization of Fe-based amorphous composite by laser direct deposition

Fe-based metallic glasses can be potential structural materials owing to their combined superior strength, excellent corrosion and wear resistance properties. In this study, synthesis of Fe–Cr–Mo–W–Mn–C–Si–B metallic glass composite with a large fraction of amorphous phase is accomplished using laser direct deposition. X-ray diffraction (XRD) and transmission electron microscopy investigations reveal the existence of amorphous structure. Microstructure analyses by optical microscopy and scanning electron microscopy (SEM) indicate the periodically repeated microstructures of amorphous and crystalline phases. Partially crystallized structure brought by laser reheating and remelting during subsequent laser scans aggregated in the overlapping area between each scan. XRD analysis showed that the crystalline particle embedded in the amorphous matrix was Cr1.07Fe18.93 phase. The periodically repeated amorphous/crystalline composite microstructure remained the same from the first to the last layer. Microhardness of the amorphous phase (HV0.2 1591) showed a much higher value than that of the crystalline phase (HV0.2 947). Similar values of wall macrohardness and phase microhardnesses indicated that the amorphous phase is the main contributor to the average hardness of laser deposited metallic glass. Wear resistance property of deposited layers showed a significant improvement with the increased fraction of amorphous phase.

Effect of Solidification Process on Magnetic Properties of Nd-Based Bulk Amorphous Forming Alloy

The magnetic behavior and structure of Nd60Al10Fe20Co10 bulk amorphous forming alloy prepared under a wide cooling rate, from 1 K/s to 105 K/s, by means of fluxing method, drop tube, suction casting and melt-spinning were studied. The samples achieved by suction casting, melt-spinning and drop tube undergo a cooling rate larger than 30 K/s, and comprise a large fraction of amorphous phase. Samples produced by fluxing method with the cooling rate in the magnitude of 1 K/s are fully crystallized. The room temperature hysteresis loops of the samples with high cooling rate show one ferromagnetic phase, which decomposes upon crystallization of the amorphous phase at about 750 K. The drop tube and fluxing samples exhibit two-phase hysteresis loops at room temperature, and the hard magnetic phase is found stable upon heating to 773 K. The crystalline hard magnetic phase in the slowly cooled sample shows comparable coercivity and Curie temperature with that of the metastable ferromagnetic phase in the amorphous alloys. These trends suggest that all phases have a similar local structure and chemical composition.

Carbide and hydride formation during mechanical alloying of titanium and aluminium with hexane

Mixtures of elemental titanium and aluminium powders of overall composition Ti x Al 1+ x ( x = 0.02, 0.3, 0.4, 0.5, 0.6, 0.7, 0.75, 0.8) were mechanically alloyed in a planetary-type ball mill. Hexane was added as a process control agent to reduce powder agglomeration during milling. The as-milled powders were characterized using X-ray diffraction, differential scanning calorimetry, scanning electron microscopy and transmission electron microscopy. During milling, the hexane is partially dissociated, with the free carbon and hydrogen incorporated within the Ti x Al 1 − x alloy powders in increasing amounts with increasing milling time. The amount of incorporated carbon increases with the initial Ti content of the powder mixture, reaching a maximum of 12 wt.% incorporated into an initial Ti 0.8Al 0.2 powder mixture after 100 h of milling. The hydrogen is found to combine with elemental Ti to form TiH 2− x , with an initial Ti 0.5Al 0.5 powder mixture milled for 40 h incorporating 0.95 wt.% H. The milled (Ti x Al 1 − x + C) powder mixtures form a large fraction of amorphous phase near x = 0.5. Annealing of the as-milled powders incorporating dissolved carbon and hydrogen produced a mixture of Al 2Ti 4C 2, TiC and TiAl.

Characteristics of nanophase TiAl produced by inert gas condensation

Nanophase TiAl, with grain sizes in the range of 10–20 nm, was synthesized by magnetron sputtering in an inert gas atmosphere and consolidated, in situ, under vacuum. The properties of the powders and sintered compacts were studied by transmission electron microscopy, scanning electron microscopy, calorimetry, Rutherford backscattering, and x-ray diffraction. Samples compacted at 1.0 GPa at room temperature had a large fraction of amorphous phase, while samples compacted at the same pressure and 250 °C were predominantly the equilibrium γ phase. An enthalpy change of 22 kJ/g-atom was measured during a DSC scan over the temperature range 125–450 °C, which is approximately the range over which crystallization occurs. Nearly full density could be achieved by sintering at 450 °C without significant, concomitant grain growth. The Vickers microhardness of these samples at room temperature and at −30 °C revealed an inverse Hall–Petch relationship at small grain sizes, 10–30 nm, and the usual Hall–Petch behavior at larger grain sizes. A small component of indentation creep was also observed. The maximum hardness is 4 times larger than that of a cast TiAl specimen of the same composition. The Vickers hardness was also observed to decrease rapidly with temperature above 200 °C.