Combustion synthesis of Al-Ti intermetallic compounds
Krzysztof Naplocha, Kazimierz Granat
Quarterly No. 4, 2009 pages 337-341
DOI:
keywords: combustion synthesis Al-Ti, perform, composite
abstract Investigations of porous Al-Ti materials produced by combustion synthesis were presented. Some of produced structures can be infiltrated with liquid aluminum alloy reinforcing castings. Synthesis and structure formation route, phase composition, degree of homogeneity and porosity sort were analyzed. Cylindrical green compacts from Al and Ti powder in Al:Ti = = 75:25, 70:30, 67:33, 60:40, 55:45, 50:50, 45:55, 28:72 stoichiometric ratio were prepared. Granularity of Al powder amounts -325, Ti powder -325 and -200. In order to prepare cylindrical specimens 23 mm in diameter and 4.5 mm high, the powder mixture was cold pressured at 484 MPa. Synthesis was conducted in special constructed microwave reactor with a quartz tube filled with argon atmosphere. Compact was ignited in waveguide under strongly focused field. Temperature were controlled using continuous regulated power supply with pyrometer Raytek, model Marathon MM. Diameter of the measuring spot was ca. 0.6 mm. The structures were examined with X-ray diffraction (XRD) and a scanning microscope JEOL JSM-5800LV with an attachment for chemical analysis EDS. Recorded temperature shows that acceleration of synthesis propagation followed after Al3Ti compound formation. Samples containing 45-55 at. % Al reached the highest synthesis temperature. During microscope investigation rounded grains with core from (Ti) solid solution were observed. These grains mainly contain AlTi3 compound, which pass into AlTi at the external edge. Almost for all kind of samples, especially with higher Al content, composition of grains was similar. Around them envelopes of AlTi and Al2Ti were formed. Chemical composition of matrix was adequate to stoichiometric ratio of initial powder mixture. XRD investigation confirmed multiphase structure and little influence on it of Ti powder granularity. Part of samples with regular structure and open porosity, containing 75, 67 and 55 at. % Al were used for production of composites with aluminium alloy matrix. Porous materials (preform) were infiltrated under 40 MPa pressure to locally reinforce casting.