Amorphous consolidation

The alloys are first produced by rapid solidification and are amorphous in nature. They are either directly fabricated as powders, by a process such as high-pressure gas atomisation (HPGA), or by melt-spinning of ribbons, which are subsequently pulverised to form a powder (<150 /im). The powders are then consolidated by hot extrusion between 950-1050°C where the initial amorphous structure breaks down and forms a fine dispersion of stable borides in a ductile Fe-based matrix. 

Yromans H, Bolhuis GK, Lerk CF, Kussendrager KD, Bosch H. Studies on tableting properties of lactose. VI. Consolidation and compaction of spray-dried amorphous lactose. Acta Pharmaceutica Suecica 1986 23(4) 231-240. 

The model PBZT/ABPBI molecular composite system is limited since the rod and the matrix do not possess glass transition temperatures for subsequent post form consolidation. In an effort to improve the processability for molecular composites, thermoplastics were used as the host matrix. Processing from acidic solvents requires the thermoplastic host to be soluble and stable in meth-anesulfonic add. Thermoplastic matrices were investigated including both amorphous and semicrystalline nylons [71,72], polyphenylquinoxaline (PPQ) [73] and polyetheretherketone (PEEK) [74], Table 5 shows the mechanical properties obtained for various processed PBZT thermoplastic molecular composite systems. As an example, the PBZT/Nylon systems showed 50-300% improvement over uniaxially aligned chopped fiber composite of comparable compositions. However, the thermally-induced phase separation during consol-... 

One of the first examples of mesoscopic-macroscopic two-dimensional ordering within a structure involved a bacterial superstructure formed from the co-aligned multicellular filaments of Bacillus subtilis that was used to template macroporous fibers of either amorphous or ordered mesoporous silica [82], The interfilament space was mineralized with mesoporous silica and, following removal of the organic, a macroporous framework with 0.5 pm wide channels remained. Mesoporous silica channel walls in this hierarchical structure were curved and approximately 100 nm in thickness. Dense, amorphous walls were obtained by replacing the surfactant-silicate synthesis mixture with a silica sol solution. The difference in the mode of formation between porous and non-porous wall structures was explained in terms of assembly from close-packed mesoporous silica coated bacterial filaments in the former compared to consolidation of silica nanoparticles within interfilament voids in the latter. 

As in the case of MgO, the powder is precalcined at temperatures of 1000-1350°C to reduce the surface area of the particles [22]. The surface area is reduced by partial elimination of porosity of individual grains and by grain growth resulting from consolidation of amorphous content. The presence of MgO and silica in zinc oxide promotes densification by forming a solid solution of ZnO with these oxides [7,23]. In addition to this densification, compounds of lower solubility formed by the solid solutions, such as zinc silicates, are likely to reduce the overall solubility of zinc oxide. 

Cylindrically converging shock waves on powders were used to make mixtures of diamonds and hBN. BN fiber reinforced Zr02 was described . A nanostructured composite of magnetic particles of FOj N in a nonmagnetic matrix of BN is made via an inorganic geP. Fabrication of BN-B4 composites was reported . Consolidation of novel sintered composites formed from high pressure crystallization of amorphous ceramics was also described. The literature discusses other ceramics reinforced with BN fibers, as welF . ... 

Figure 7 shows densification of five layered compacts graded from amorphous TiAl to PSZ via temperature gradient controlled electric discharge resistance consolidation using the stepped graphite die as shown in Fig.4. The consolidation of FGMs having hf = 7.40 and 6.52 under two different temperature gradient show...

HPT has been successfully applied for microstructure refinement in metals, alloys and not long ago in composites and in semiconductors [17,18], as well as consolidation of nanopowders [7], Among new developments in HPT processing we would like to emphasize also the observation of SPD-induced nanocrystallization in initially amorphous alloys producing nanocrystalline materials with a grain size of 10-15 nm [19],... 

CONSOLIDATION OF CU AND AMORPHOUS ZR-BASED POWDERS BY SEVERE PLASTIC DEFORMATION... 

Abstract Consolidation of amorphous Zr-based and Cu nanoparticles is achieved by... 

Advances in the production of amorphous and nanostructured powders over the past decade have given materials scientists new opportunities for the creation of high strength bulk materials. Bulk material with extraordinary properties should result if such powders can be consolidated without significant changes to the microstructure, and strong interparticle bonding is achieved. There are several methods available to consolidate... 

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