Zirconium Dodecaboride-based cutting material

Abstract

621.785;621.9.825.7 Samples of zirconium dodecaboride are obtained by means of arc and induction melting of a mixture of zirconium and boron powders. A solder for binding the zirconium dodecaboride to the steel holder of the tool is selected. It is established that cutting tools supplied with zirconium dodecaboride may be used in operations of finish turning of adhesive-active titanium alloys.Among the different alloys of the zirconium C boron system, zirconium dodecaboride (ZrB 12 ) is known as a material possessing rather high abrasion properties. ZrB 12 may be used especially effectively in polishing titanium and titanium alloys [1,2]. Zirconium dodecaboride is produced by arc melting of a charge of prescribed composition. The ingot that has been formed in a crystallizer is crushed in order to obtain abrasive powders of different grain sizes. The abrasive disks that are produced from these powders have demonstrated not only a high degree of efficiency in the treatment of the titanium alloy VT-1 comparable with that of diamond disks of the same grain size, but also yield a significant decrease in the surface roughness of the worked part [3].In view of the high abrasive capacity of zirconium dodecaboride, it is of significant scientific and practical interest to study the possibility of creating on the base of zirconium dodecaboride, not only grinding tools, but also cutting tools. The goal is to apply these types of tools for turning titanium and titanium alloys, in view of the fact that articles made of these materials are now finding increasingly greater use. The possibility of creating a cutting tool with inserts provided with polycrystals of zirconium dodecaboride has been studied by analogy with the well-known technology of fabricating cutting tools with inserts provided with polycrystals of superhard materials [4,5].Rugged cutting elements of ZrB 12 have been fabricated using arc (type I) or induction (type II) melting. Arc melting of compacts from a mixture of powders of zirconium and boron of stoichiometric composition have been produced in a standard laboratory-scale furnace equipped with a copper water-cooled crystallizer and nonconsumable tungsten electrode in a purified argon medium. From the melting point (2082EC) to a temperature of around 1500EC the cooling rate amounted to roughly 400 deg/sec and was then gradually reduced to 150 deg/sec until the ingot had completely cooled down. Directed crystallization of the melt was achieved in a Kristall III induction plant following the formation of a fusion zone at a temperature corresponding to the phase diagram of Zr − B. Preliminarily sintered porous rod billets were used as the initial material for directed crystallization. The charge was in the form of a mixture of zirconium powder and powder of finely crystallized boron. The boron was taken in excess with respect to stoichiometry. The components of the charge were carefully mixed in a cavitation bath of an ultrasonic vibrator. Rods were compacted from the obtained mixture in a steel die pressur...

Synthesis and Characterization of Single-Phase Metal Dodecaboride Solid Solutions: Zr1–xYxB12 and Zr1–xUxB12

“…The ability to synthesize a single phase metal dodecaboride at stoichiometric metal to boron ratios (accounting for boron evaporation during arc-melting) by means of a solid-solution formation allows for a much easier synthesis of possible tools and abrasives and their superior properties due to both solid-solution hardening (mechanical properties) and better thermal conductivity (due to having only grains of one phase). 38 The only other methods for producing "phase pure" metal dodecaborides are: having excess boron (M : B = 1 : 20), which results in a considerable amount of boron-rich phases; and zone (induction) melting, although producing single crystals with exact stoichiometry is not easily scalable; furthermore single crystals have inferior mechanical properties than their polycrystalline counterparts. [26][27][28][29]38 Upon the addition of carbon to the dodecaboride system, a change in the relative quantity of secondary phases can be observed (Table 2, Figure 2).…”

“…38 The only other methods for producing "phase pure" metal dodecaborides are: having excess boron (M : B = 1 : 20), which results in a considerable amount of boron-rich phases; and zone (induction) melting, although producing single crystals with exact stoichiometry is not easily scalable; furthermore single crystals have inferior mechanical properties than their polycrystalline counterparts. [26][27][28][29]38 Upon the addition of carbon to the dodecaboride system, a change in the relative quantity of secondary phases can be observed (Table 2, Figure 2). The change of the unit cell parameters for the MB12 phase upon the addition of yttrium and carbon can be seen in Table 3.…”

“…36,37 This severely limits their potential applications in tooling and as abrasives, due to having either boron-rich phases, which can form boride phases with the binder metals, or having the soft lower boride phases (ZrB 2 and YB 6 ), which hinder the mechanical properties and also reduce the thermal conductivity of the material and as such heat removal from the tool edge. 38 Metal dodecaborides can be synthesized as single crystals via zone melting, which is not easily scalable. 38 However, using solid solution alloying, here we have synthesized a single-phase metal dodecaboride phase, Zr 0.5 Y 0.5 B 12 and Zr 0.5 U 0.5 B 12 , as confirmed by powder XRD, scanning electron microscopy (SEM) and solid-state NMR spectroscopic data.…”

“…38 Metal dodecaborides can be synthesized as single crystals via zone melting, which is not easily scalable. 38 However, using solid solution alloying, here we have synthesized a single-phase metal dodecaboride phase, Zr 0.5 Y 0.5 B 12 and Zr 0.5 U 0.5 B 12 , as confirmed by powder XRD, scanning electron microscopy (SEM) and solid-state NMR spectroscopic data. The fact that these alloys are single phase not only makes it easier to study their properties, but also in the case of mechanical properties has the added benefit of solid solution hardening resulting in enhanced hardness, i.e.…”

Superhard Mixed Transition Metal Dodecaborides

“…Apart from the fundamental interest of metal MB 12 due to their unique structure, their properties are also of interest in industrial applications, such as Zr-based cutting tools and abrasives (with abrasive qualities comparable to that of diamond, but producing less roughening of surfaces). 33 Therefore, mechanical properties (superhardness), being lightweight (due to density comparable to or lower than that of diamond (3.52 g/cm 3 )), and enhanced oxidation resistance properties are of interest for potential applications in machining industries and as lightweight protective coatings. Here, we examine the parent structure of the most common metal dodecaborides by creating solid solutions and speculate on the mechanism behind a cubic to body-centered tetragonal phase transformation.…”