Ti-B alloys

THE MICROSTRUCTURE AND MARTENSITIC TRANSFORMATION IN A (POTENTIALLY) SHAPE MEMORY Ni-AI-Ti-B ALLOY... 

Key words structural efficiency metal matrix composite amorphous metals, superhigh strength Al, nanocrystalline metals, Ti-B alloys... 

A number of parallel future efforts are required in the Ti-B alloy system. The primary objective of future work is to eliminate primary TiB. Efforts to optimize processing to achieve the balance of first and second tier mechanical properties required for fracture-critical applications are also underway. Ti-B alloys may be considered as a matrix for continuously reinforced Ti MMCs, where the exceptional specific strength and stiffness of Ti-B alloys may help overcome current weaknesses in Ti-MMCs. In addition to the Ti-B alloys discussed here, exploration and development of similar in-situ eutectic composites are underway. Specifically, extensive efforts on the Ti-Si system are being pursed [12], and results similar to those reported here are now being obtained. These results are discussed in detail elsewhere in this volume. 

Figure 4. Tensile properties of wrought Ti-6A1-4V and extruded Ti-B alloys produced via prealloyed and blended elemental powder approaches. The loading axis is parallel to the extrusion direction. BE signifies material produced by the blended elemental approach. All compositions are in weight percent.

The incipient temperature of sharp softening is defined by a titanium matrix composition in full and can be increased by rational alloying from 500°C for the binary Ti-B alloy to 650°C. 

Figure 12.6. (a) Calculated (a + a) phase boundary for Fe-V together with experimental boundaries (After Spencer and Putland 1973). (b) Comparison between calculated and experimental values of the concentration of Al, V and Fe in the two phases in Ti-6AMV alloy (after Saunders and... 

Fig. 33. Selected area diffraction patterns of Ti-Al alloys taken on the [001] zone axis which show the increasing relative intensity of the superlattice reflections with increasing Ti content (a) 3 a/o Ti, (b) 5 a/o Ti, (c) 16 a/o Ti, and (d) 24 a/o Ti. A labeled schematic of the diffraction pattern is shown [188],...

B. Koklic and M. Veber, Influence of sampling to the homogeneity of Cu-Ti-Zn alloy samples for the analyses with glow discharge optical emission spectroscopy, Accredit. Qual. Assur., 8(3 4), 2003, 146-149. 

As we discussed in the previous section, Cu addition is quite effective in preventing the formation of compounds in B-rich Fe-Zr-B alloys. This approach is also effective for the Fe93 xM7Bx (M= Ti, Ta and W) alloys. The formation of the tetragonal-Fe3B phase upon primary crystallization in these amorphous alloys is suppressed completely by an addition of 1 at% Cu. As a result, pe > 104 at 1 kHz has been confirmed for nanocrystalline Fe82Ti7B10Cui and Fe82Ta7B10Cui [7]. 

Figure 11.2. Al NMR spectra of Ti-Al alloys showing the effects of particle reduction by filing and stress release by annealing at different temperatures. Spectra A-B, Tio.52Alo.48. Spectra C-E, Tio.6oAlo.4C). From Smith et al. (1996) by permission of the copyright owner.

The volume fraction of reinforced phase in eutectics is 7.7 % and 31-wol.% for systems Ti-B and Ti-Si, respectively. The typical structures of eutectic alloys for Ti-Si system is shown in Fig. 2. According to binary diagrams of phase equlibria, an essential solubility of silicon in a- and 13-phases is observed, which is dependent on temperature there is an eutectoid transformation (in this respect diagram Ti-Si is similar to Fe-C diagram), but in system Ti-B essential solubility of boron in a- and 3- phases does not occur. For this reason the structure of composites of Ti-B system is more stable at temperature variation. 

Figure 4. TEM image of as-cast Ti-B-Si alloys. Fine silicoborides are clearly visible.

System Ti-B-X represents a basis for development of alloys with a high stiffness, especially at additional alloying with aluminum [24], Titanium boride has high Young modulus and simultaneously it is practically insoluble in titanium matrix. Aluminum is one of few elements, which being dissolved in titanium increases Young modulus of matrix. 

The further progress can be related to the development of alloys of Ti-B-Si-X system. Preliminary study of these alloys has shown an availability of some additional early unknown phase. In addition to typical lamellar borides visible in structure of the alloys is extremely disperse phase having boron and silicon in its composition. Electron microscopy image of this phase is shown in Figure 4. Structural identification of this silicoboride is not completed yet, however it is already possible to note appreciable increase of stiffness of the alloys at simultaneous presence of boron and silicon (Table ) ... 

Ti-B-X systems alloys are promising for achievement of high specific stiffness. 

Ti-B-Si-X alloys, where X is Al, Zr etc, is a promising system to achieve a good combination of high specific stiffness, specific strength and heat resistance. 

Figure 1. (a) Room temperature elongation, and (b) tensile strength, UTS of binary Ti-Si-alloys vs. silicon content. Literature data is [6],... 

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