Amorphous Structure Phase Research Articles

Cu–Pd–B Alloy Nanoparticles Synthesized by External Boron Doping Method

Abstract We present a new synthetic approach for Cu–Pd–B nanoscale alloys. Crystalline face-centered cubic Cu–Pd–B alloy nanoparticles were successfully obtained via an amorphous structure phase caused by external heavy B doping. Elemental mapping with simultaneous energy-dispersive X-ray spectroscopy and energy loss spectroscopy in a scanning transmission electron microscope revealed a solid-solution structure composed of the three elements.

Characterization and hardness enhancement of amorphous Fe-based metallic glass laser cladded on nickel-free stainless steel for biomedical implant application

Amorphous metals – or Metallic Glass (MG) – have a great potential in bone implant applications because of their exceptional mechanical properties, excellent tribological and corrosion resistance characteristics, and good biocompatibility. An upcoming trend is to develop an amorphous metallic coating on different metallic alloys to promote the hardness of crystalline metallic alloys. In this work, Fe-based amorphous – FeCrMoCB – coating was developed on nickel-free stainless-steel substrate using laser cladding (LC) technique at two laser power levels (1500 and 2000 W) with different scanning speeds to enhance the hardness of the crystalline metallic substrate. Scanning electron microscope (SEM) and X-ray diffraction (XRD) examinations confirmed the formation of both the amorphous structure phase at the coating layer (CL) and crystalline structure phase at the transition layer (TL) at the interface. The experimental results showed that all specimens confirmed amorphous CL. However, at relatively low speed, 5 mm/s at 1500 W and 15 mm/s at 2000 W, the CL exhibited higher crystallinity within the amorphous structure. The micro-hardness was extremely high within higher amorphous content (up to 1300 HV0.1), while the hardness value was degraded when higher crystallinity existed (900 HV0.1). It was noticed that for similar CL microstructure and hardness values, increasing the laser power by 33.33% exhibited increasing the scanning speed by 150%–200%. This indicates the significant effect of the laser power on the microstructure and the hardness of the CL. In addition, the laser power and scanning speed has an interaction effect on the CL developed.

Molecular dynamics simulation of silicon carbide nanoscale material removal behavior

The scratching processes of monocrystalline and polycrystalline silicon carbide (SiC) with diamond grit were studied by molecular dynamics simulation to investigate the nanoscale material removal behavior. The results showed that, for both monocrystalline and polycrystalline SiC, the material removal processes were achieved by the phase transition to the amorphous structure. Large depth of cut and low scratching speed induced the large scratching forces, stress, and surface damage layer thickness. Less amorphous structure phase transition, smaller normal scratching force, and higher tangential stress were found in polycrystalline SiC, comparing to the monocrystalline SiC, due to the material soften caused by the microstructure, under all scratching conditions. Furthermore, the tangential stress showed highly dependent on the grain geometry and grain boundary (GB) location in polycrystalline. The subsurface damage layer in polycrystalline was little thinner than that in monocrystalline before the new GB generation at a low depth of cut and deteriorated at large depth of cut. In addition to the plastic deformation, which occurred in the monocrystalline SiC nanoscale scratching, the intergranular fracture and transgranular fracture were also observed through the GB generation and connection in polycrystalline SiC.

Atomic pair distribution function analysis of materials containing crystalline and amorphous phases

Abstract The atomic pair distribution function (PDF) approach has been used to study the local structure of liquids, glasses and disordered crystalline materials. In this paper, we demonstrate the use of the PDF method to investigate systems containing a crystalline and an amorphous structural phase. We present two examples: Bulk metallic glass with crystalline reinforcements and Fontainebleau sandstone, where an unexpected glassy phase was discovered. In this paper we also discuss the refinement methods used in detail.

The Li xMPn 4 phases (M/Pn = Ti/P, V/As): new negative electrode materials for lithium ion rechargeable batteries

Li x TiP 4 ternary phases ( x=7 and 9) show very close electrochemical behaviors versus lithium compared to the previously reported Li 9VAs 4 and Li 7VP 4. Up to seven lithium ions reversibly react with Li 9TiP 4, leading to specific and volumetric capacities of 970 mAh/g and 1650 mAh/cm 3, respectively, at average potentials close to 1 V. Galvanostatic and potentiodynamic experiments reveal that lithium extraction/insertion follow different mechanisms: a two-phase process is evidenced on charge whereas a more complex process is achieved on discharge. Besides, in situ X-ray diffraction (XRD) patterns show that both Li 9TiP 4 and Li 9VAs 4 undergo a reversible crystalline to amorphous structural phase transition upon cycling.

Ion induced phase precipitation and growth in thin films: Fractals and dendrites

This paper describes ion induced phase precipitation and growth of fractal or percolation infinite clusters during amorphous structural phase transition and dendritic behaviour during crystalline-to-amorphous phase transition in NiMo, NiAl and AuTi thin solid films. Experimental evidence revealed that the fractal clusters were formed through a multinucleation process. The randomly distributed large clusters grown from the nuclei gave rise to an attractive growth at the unstable active zones. The detailed observations and computer modeling are described.

Some new structural transformations induced by ion beams

Upon ion beam irradiation, some new phenomena were observed in thin solid films during crystal-amorphous or amorphous-crystal transition. Quasicrystalline AlFe phase was formed in an amorphous matrix by ion beam mixing of AlFe multilayers without post-annealing. In the NiMo systems, dendritic growth was detected when alloy films were transformed from crystalline to amorphous, while fractal patterns and percolation network structures of single crystal precipitates were observed, for the first time, at critical conditions of amorphous structural phase transitions. The dimensions of the ion-induced patterns was determined by image processing computer to be 1.72 ± 0.07 and 1.63 ± 0.06, respectively. The pattern growth was also studied in some other metal systems and various patterns were observed. In this paper, experimental observations are presented and the implications of these results are also discussed.

Percolation scale effects upon amorphous structural phase transition in an alloy film

Percolation scale effects upon amorphous structural phase transition in an alloy film

Percolation scale effects upon amorphous structural phase transition in an alloy film

Percolation structures are formed during the amorphous-to-crystalline phase transition induced by ion beam irradiation in Ni-Mo alloy films. It is found that the percolating networks emerged at the critical point of the transition and they were well fitted for the percolation scales. The direct observations, in this study, provide the evidences of the percolation behaviours upon such a phase transition in thin solid films.

FRACTAL GROWTH OF NICKEL-BASED ALLOYS IN THIN FILMS

In this article, we report the formation of fractal structures in nickel-based alloy systems, in thin films during ion beam-solid interactions. The experimental results show that a necessary condition for the fractal growth in thin films is amorphous structural phase transition in the amorphous matrix. The fractal dimensions of the observed patterns depended on the specific alloy systems: Df = 1.4 for Ni-Zr system and Df=1.7 for Ni-Mo system. The relationship among ion-solid interaction, amorphous structural phase transition and the fractal growth in thin films is also discussed.