Unmelted TiC Research Articles

Microstructure and fatigue properties of plasma transferred arc alloying TiC-W-Cr on gray cast iron

In this paper, TiC-W-Cr powders were alloyed on grey cast iron by plasma transferred arc (PTA). The alloying samples were characterized the microstructure, microhardness, fatigue life and fatigue crack growth. From the results, it is indicated that two distinguishing region: alloying zone, heat affected zone are formed on the surface after PTA alloying. The alloying zone mainly consists of primary austenite, martensite, a eutectic of (Fe,Cr) 7C 3 carbide and austenite as well as the uniformly distributed un-melted TiC particles. PTA alloying TiC-W-Cr eliminates the stress concentration at the edge of graphite and produced hard carbide, resulting in frequent crack deflection. As a result, the Weibull distribution of fatigue life demonstrates that PTA alloying TiC-W-Cr exhibits longer lives compared to matrix and PTA hardening without reinforcement, but more scattered. In addition, on the basis of the careful observation of fatigue crack growth, it is shown that the fatigue crack growth rate could be retarded by PTA alloying TiC-W-Cr at low stress intensity.

High temperature mechanical properties of a laser melting deposited TiC/TA15 titanium matrix composite

The tensile behavior of a laser melting deposited TA15 titanium matrix composite containing 10 vol.% TiC reinforcement was studied at elevated temperatures. Results showed that the composite exhibited a superior strength but lower tensile elongation than monolithic matrix alloys at 873 K. As the test temperature increased from 873 K to 973 K, the ultimate tensile strength of the composite decreased from approximately 625 MPa to 342 MPa while the elongation rose from 7% to 18%. The internal damage phenomena were more evident at higher temperatures during tensile deformation. Although there was an increasing damage of interface debonding with the increasing test temperature, the fracture mechanism of the composite was predominantly controlled by particle cracking followed by ductile failure of the matrix in the whole temperature range of 873–973 K. This could be attributed to the strong bonding of the as-solidified TiC reinforcements with the matrix at high temperatures and the existence of prone-to-fracture carbides such as coarse unmelted TiC and clustered TiC particles in the composite.

Compositionally graded Ti6Al4V + TiC made by direct laser fabrication using powder and wire

Ti6Al4V reinforced with TiC has been fabricated as compositionally graded material by direct laser fabrication using TiC powder and Ti6Al4V wire which were fed simultaneously into the laser focal point. The microstructure along the length of the sample has been characterised using X-ray diffraction and scanning electron microscopy. The results show that the composition along the length changes as expected from the imposed changes in feed rate when allowance is made for the different capture efficiency for the powder and the wire. Some unmelted TiC has been observed in regions where the TiC fraction was high, but along most of the length of the samples TiC was completely melted and formed primary TiC, eutectic TiC and secondary TiC. Some preliminary tribological properties of the compositionally graded material were obtained using a sliding wear test which showed that the tribological properties of Ti6Al4V are improved by the reinforced TiC particles with the optimum frictional behaviour being found with approximately 24 vol% of TiC.

Laser synthesizing NiAl intermetallic and TiC reinforced NiAl intermetallic matrix composite

The NiAl intermetallic layers and NiAl matrix composite layers with TiC particulate reinforcement were successfully synthesized by laser cladding with coaxial powder feeding of Ni/Al clad powder and Ni/Al+TiC powder mixture, respectively. With optimized processing parameters and powder mixture compositions, the synthesized layers were free of cracks and metallurgical bond with the substrate. The microstructure of the laser-synthesized layers was composed of β-NiAl phase and a few γ phases for NiAl intermetallic; unmelted TiC, dispersive fine precipitated TiC particles and refined β-NiAl phase matrix for TiC reinforced NiAl intermetallic composite. The average microhardness was 355 HV0.1 and 538 HV0.1, respectively. Laser synthesizing and direct metal depositing offer promising approaches for producing NiAl intermetallic and TiC-reinforced NiAl metal matrix composite coatings and for fabricating NiAl intermetallic bulk structure.