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The goal of this work was to study the phase and microstructure changes involved in the process of coating formation by detonation spraying of Ti3Al, TiAl, and TiAl3intermetallics. The O2/C2H2ratio was varied between 1.1 and 2.0, and the explosive charge was 30–40% of the barrel volume. In most experiments air was used as a carrier gas; selected experiments were performed with argon. We found that depending on the spraying parameters, TiAl3essentially retains in the coatings or partially decomposes forming TiAl and Ti3Al as minor phases. Detonation sprayed Ti3Al reacts with nitrogen and oxygen partially transforming into titanium nitrides TiN/Ti2N and titanium oxynitrides TiNxOy. TiAl partially decomposes forming Ti3Al, which further reacts with oxygen and nitrogen as the particle temperature and the content of oxygen in the explosive mixture increase. Thein situformed titanium nitrides and oxynitrides show a reinforcing effect increasing the hardness of the coatings. [ABSTRACT FROM PUBLISHER]

We present several possible microstructure development scenarios in Ti 3SiC 2-Cu composites during mechanical milling and Spark Plasma Sintering (SPS). We have studied the effect of in situ consolidation during milling of Ti 3SiC 2 and Cu powders and melting of the Cu matrix during the SPS on the hardness and electrical conductivity of the sintered materials. Under low-energy milling, (3–5) vol.%Ti 3SiC 2-Cu composite particles of platelet morphology formed, which could be easily SPS-ed to 92–95% relative density. Under high-energy milling, millimeter-scale (3–5) vol.%Ti 3SiC 2-Cu granules formed as a result of in situ consolidation and presented a challenge to be sintered into a bulk fully dense sample; the corresponding SPS-ed compacts demonstrated a finer-grained Cu matrix and more significant levels of hardening compared to composites of the same composition processed by low-energy milling. The 3 vol.% Ti 3SiC 2-Cu in situ consolidated and Spark Plasma Sintered granules showed an extremely high hardness of 227 HV. High electrical conductivity of the Ti 3SiC 2-Cu composites sintered from the granules was an indication of efficient sintering of the granules to each other. Partial melting of the Cu matrix, if induced during the SPS, compromised the phase stability and uniformity of the microstructure of the Ti 3SiC 2-Cu composites and thus it is not to be suggested as a pathway to enhanced densification in this system. [ABSTRACT FROM AUTHOR]

Abstract: We have examined the new phase formation and compositional variations in the coatings produced by detonation spraying of Ti3Al powders in atmospheres of different chemistry. The composition of the spraying atmosphere was varied by changing the O2/C2H2 ratio used for the detonation. In the coatings sprayed at an O2/C2H2 ratio of 0.87 and 1.05, certain deviations of the Al/Ti ratio have been observed relative to the sprayed powder. In these coatings, the Ti3Al phase was found along with TiN and Ti2N formed due to the reaction of the heated particles with nitrogen used for powder injection. The amount of TiN increased with increasing explosive charge and a concomitant rise in the particles temperature. Under O2/C2H2 ratios equal to 1.50 and 2.00, significant losses of Al were detected, the coatings being composed mainly of titanium oxides. This study shows that detonation spraying conditions excluding severe oxidation of Ti3Al can be found as well those facilitating oxidation with an associated loss of Al in the deposits. [Copyright &y& Elsevier]

Abstract: In the present work, rutile powders containing additions of metallic silver (2.5vol.%) were detonation sprayed in a reducing atmosphere formed by gaseous detonation products of the C2H2 +1.05O2 mixture. The initial volume of the C2H2 +1.05O2 mixture – explosive charge – used for a detonation pulse was computer-controlled as the fraction of the barrel volume filled with the mixture. Using a previously developed model of the detonation process, the particle temperatures and velocities were calculated to explain the observed phase and microstructure development in the coatings. With increasing explosive charge, the temperature of the sprayed particles increased and rutile was partially reduced to oxygen-deficient TiO2−x and then to Ti3O5. When the melting temperature of rutile was not reached, the coatings were porous; semi-molten particles formed denser coatings obtained with higher spraying efficiency. Silver inclusions in the titanium oxide matrix experienced melting and substantial overheating, but remained well preserved in the coatings. [Copyright &y& Elsevier]