Boride alloys

K. I. Portnoi, G. V. Samsonov. Boride Alloys, Izd. GNKT RSFSR, Moscow,... 

AH of the alloys Hsted in Tables 4 and 5 are austenitic, ie, fee. Apart from and soHd-solution strengthening, many alloys benefit from the presence of carbides, carbonitrides, and borides. Generally the cubic MC-type monocarbides, which tend to form in the melt, are large and widely spaced, and do not contribute to strengthening. However, the formation, distribution, and soHd-state reactions of carbides are very important because of their role... 

The materials deposited by PVD techniques include metals, semiconductors (qv), alloys, intermetaUic compounds, refractory compounds, ie, oxides, carbides, nitrides, borides, etc, and mixtures thereof. The source material must be pure and free of gases and inclusions, otherwise spitting may occur. 

Boron forms B—N compounds that are isoelectronic with graphite (see Boron compounds, refractoryboron compounds). The small size also has a significant role in the interstitial alloy-type metal borides boron forms. Boron forms borides with metals that are less electronegative than itself including titanium, zirconium, and hafnium. 

Uses. In spite of unique properties, there are few commercial appUcations for monolithic shapes of borides. They are used for resistance-heated boats (with boron nitride), for aluminum evaporation, and for sliding electrical contacts. There are a number of potential uses ia the control and handling of molten metals and slags where corrosion and erosion resistance are important. Titanium diboride and zirconium diboride are potential cathodes for the aluminum Hall cells (see Aluminum and aluminum alloys). Lanthanum hexaboride and cerium hexaboride are particularly useful as cathodes ia electronic devices because of their high thermal emissivities, low work functions, and resistance to poisoning. 

In general, many metals and alloys (e.g. of Al, Ta and Mo) can be deposited on metallic and some non-metallic substrates. M may also be a metal compound having special useful properties (e.g. borides, nitrides, oxides, silicides and carbides), or even a non-metal such as Si (as in Ihrigising ). 

Figure 2. (b) Formation and lattice parameters of perovskite borides M gPdjB. B content from as-cast alloys ", = La. Ce, Pr, Eu, Gd, Dy. 

Metal oxides, metal sulfides, metal nitrides, metal carbides, metal borides, metal alloys, metallic glasses, molecular sieves, salts, acids... 

The reductive cleavage of the N-O bond in the isoxazolidine 162 unmasks the 1,3-amino alcohol moiety. Thus, isoxazolidines can be viewed as direct precursors of 7-amino alcohols. The reductive cleavage of the cycloadduct proved difficult. W2 Raney-Ni and nickel boride were both ineffective. In contrast, nickel-aliminium alloy in an alkaline medium efficiently reduced the N-O bond at room temperature in the presence of a base (Equation 27) <1997TA109>. 

Tungsten alloy machine chips, 25 371 Tungsten blues, 25 381 Tungsten borides, 25 386 Tungsten bromide... 

The main difficulty is to prevent pyrohydrolysis over the long experimental periods. (Moisture is removed by "gettering with hot lanthanides or actinides.) The potentials of M/MF reference electrodes have also been used to study activities of metals in alloys, carbides, and borides (208). The accuracy is limited by reproducibility of potentials (2 1 mV) as a fraction of the cell potential and indeterminate errors. The latter can be avoided by checking for internal consistency (e.g., measuring emfs of two cells against a common third electrode). 

In the same way the equation for the determination of the specific magnetization of boride FesB was obtained. This phase is formed during the crystallization amorphous alloy Fes2Si2Bi6. As we found the specific magnetization of boride FesB is 192 TllO" cmVm. This value is in 1,5 times greater then the specific magnetization of cementite G-FesC and 1,1 times lower then the specific magnetization of a-iron. 

Rapidly solidified in-situ metal matrix composites. A design project for alloys based on the Fe-Cr-Mo-Ni-B system, and produced by rapid solidification, was undertaken by Pan (1992). During processing a mixture of borides is formed inside a ductile Fe-based matrix which makes the alloys extremely hard with high moduli. These alloys provide a good example of how phase-diagram calculations were able to provide predictions which firstly helped to identify unexpected boride formation (Saunders et al. 1992) and were ultimately used in the optimisation of the modulus of a shaft material for gas turbines (Pan 1992). 

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. 

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