Development of TiB and nanocrystalline Ti-reinforced novel hybrid Ti nanocomposite produced by powder metallurgy

Titanium monoboride (TiB) whisker-reinforced titanium (Ti) matrix composites were produced by powder metallurgy, through vacuum sintering. TiB is formed by thermal decomposition of TiB2 precursor. In addition, a new hybrid composite was developed by admixing nanograined and nanocrystalline (more important) Ti to enhance the transformation mechanism of TiB2 to TiB phase. The morphology and particle size of the initial powders, mixtures and the microstructure of the composites have been studied by scanning electron microscopy (SEM). The phase analysis and transformation monitoring were performed by X-ray diffraction (XRD). The sintered composites were also subjected to compressive strength and hardness measurements. According to XRD results, through the addition of nanocrystalline Ti, a probable enhancement of the TiB2 → TiB transformation occurred producing more TiB whiskers in the hybrid composites. All samples of the hybrid composites exhibited improved yield strength (1365 MPa) and hardness (358 HV) compared to the non-hybrid ones 927 MPa and 254 HV, respectively. Graphical abstract

Influence of Ti and B powder mixing modes on mixture properties and SHS composite microstructure

The paper studies the influence of mixing modes for titanium and boron powder mixtures with the 81.5 % Ti + 18.5 % B composition in a ball mill on the process characteristics of mixtures, combustion parameters, and microstructure of SHS composites. It is shown that the dependence of the electrical resistivity on the density of charge compacts for the composition under study can be used as a criterion for mixing quality, mixture uniformity. It is noted that an increase in the grinding media mass includes the mechanism of mechanical activation (MA) of mixtures. Dependences of the burning speed and temperature on density were obtained for all the mixtures under study. Burning speeds for mixtures subjected to mechanical activation (Мch/Мball = 1 : 7; 1 : 12) and without it (Мch/Мball = 1 : 4) differ significantly. Mechanically activated mixtures feature by differences in burning speeds depending on the charge compact thickness. Thin compacts burn at a higher speed. The burning speed of mixtures without MA (in case of smaller grinding media masses) does not depend on the compact thickness. Maximum burning temperatures of all the mixtures studied have insignificant differences depending on the density, mixing time and grinding media mass. There was also no any effect of the compact thickness on the burning temperature observed. The structure of SHS composites depends on mixing modes. The finely dispersed structure of composites with titanium diboride grains (less than 1 μm) and a titanium-based binder phase can be obtained only from MA mixtures. Alloys with a structure consisting mainly of elongated titanium monoboride grains (up to 40 μm) and a binder phase of a solid solution of boron in titanium were synthesized of the mixtures for which mechanical activation processes are not essential.

Free SHS-compression method for producing large-sized plates from ceramic materials

Large-sized plates (120×80×8 and 80×40×8 mm) were obtained from a material based on titanium monoboride by the method of free SHS-compression using press equipment with a force of up to 120 kN. The structural features of the obtained materials, their physicomechanical properties were investigated, the samples were annealed in an oxidizing environment for 10 hours at 1100 ° C.

Synthesis and electron beam facing of TiB – TiC – titanium matrix hybrid composite powders

TiB – TiC – titanium matrix composite powders have been synthesized by self-propagating high temperature synthesis (SHS) in titanium, boron and carbon reactive powder mixtures. A target volume content of the titanium matrix (binder) in the powders was 50%. The SHS powders were cladded on VT1-0 titanium sheet by electron beam facing. A thickness of the cladded coatings varied from 1 to 3 mm depending on the pass number. A phase composition and a structure of the SHS powders and of the cladded coatings were invetigated be X-ray diffraction, optical and scanning electron microscopy. According to structure investigation and hardness profiles in the “coating – titanium base plate” transition zone an adhesion of the coating to the base is high. The hardness and abrasive wear resistance tests of the cladded coatings were carried out depending on the powder used for cladding. The maximum hardness increase of the coatings strengthened by titanium monoboride and titanium carbide inclusions is 2.2 times and abrasive wear resistance – 4.3 times as compared with VТ1-0 base. According to authors’ earlier results enhance hardness and abrasive wear resistant effects of titanium matrix by titanium carbide particles and titanium monoboride is near to the wear resistance of coatings deposited with SHS TiB + Ti powder, but ~5 times less than the wear resistance of coatings surfaced with SHS powder TiC + Ti.

Synthesis and electron beam facing oftitanium monoboride – titanium matrix composite powders

Titanium monoboride – titanium matrix composite powders have been synthesized by self-propagating high temperature synthesis (SHS) in titanium and boron reactive powder mixtures. Titanium matrix (binder) content varied from 20 to 60%. The SHS powders were cladded on VT1-0 titanium sheet by electron beam facing. Cladded coatings’ thickness varied from 1 to 3 mm depending on the pass number. Phase composition and structure of powders and coatings were investigated by X-ray diffraction, optical and scanning electron microscopy. According to structure investigation and hardness profiles view in the “coating – titanium base plate” transition zone an adhesion of the coating to the base is high. The hardness and abrasive wear resistance tests of the cladded coatings were carried out depending on the powder used for cladding. The maximum hardness of the coatings strengthened by eagle-like titanium monoboride inclusions as compared with VТ1-0 base increases 2.2 times and abrasive wear resistance 3.7 times. According to previously obtained results hardening and abrasive wear resistance of titanium monoboride is much weaker than that of titanium carbide: hardness increases 1.7 times, wear resistance 5.8 times.

Commensurate Intergrowths in Titanium Monoboride Precipitates

Extended abstract of a paper presented at Microscopy and Microanalysis 2006 in Chicago, Illinois, USA, July 30 – August 3, 2006

Processing and characterization of Ti–B-based functionally graded materials produced by microwave-activated combustion synthesis

Single as well as graded compositions were fabricated in the Ti–B system using a microwave-activated combustion synthesis (MACS) process. When synergistically combined with microwave processing, combustion synthesis offers great potential for the fabrication of ceramic structures and composites. Combustion waves were triggered using a SiC susceptor to initially absorb microwaves. The effects of processing variables, such as thermal insulation, and atmosphere on the process were investigated. Examination of reacted samples by means of x-ray diffraction indicated the presence of titanium monoboride and diboride along with unreacted titanium. Compared with conventional combustion synthesized products, MACS resulted in smaller pores. However, the total amount of porosity remained almost the same. The microstructure of the graded layers and interfaces were examined using optical and scanning electron microscopy. Over the entire cross section, the interfaces were continuous and crack free.