In Situ Synthesis of TiC-Fe Composite Overlays from Low Cost TiO 2 Precursors Using Plasma Transferred Arc Deposition
- PDF / 580,175 Bytes
- 6 Pages / 593.972 x 792 pts Page_size
- 39 Downloads / 179 Views
Peer Reviewed
In Situ Synthesis of TiC-Fe Composite Overlays from Low Cost TiO2 Precursors Using Plasma Transferred Arc Deposition Santiago Corujeira Gallo, Nazmul Alam, and Robert OÕDonnell (Submitted September 16, 2013; in revised form November 10, 2013) A direct conversion of TiO2 into TiC during plasma transferred arc deposition is a cheap and novel approach to produce wear resistant coatings. The present study explored the use of a low cost titanium ore as precursor for titanium carbide in metal matrix composite overlays. The deposited layers were characterized using optical microscopy, scanning electron microscopy, x-ray diffraction and microhardness testing. A carbothermic reduction of the titanium oxides took place during the deposition of the coating by plasma transferred arc. The overlays produced in this way consisted of fine titanium carbides evenly dispersed in an iron matrix. The opportunities and limitations of this approach are discussed.
Keywords
composites, microhardness, microstructure, plasma transferred arc, reactive spraying, titanium carbides, x-ray diffraction
substitution of C for O (TiCxOy) until completion (Ref 7) according to the following simplified reaction (Eq 1): TiO2 þ 3C ! TiC þ 2CO
1. Introduction The synthesis of composite materials in situ during hardfacing has recently opened new possibilities in surface engineering (Ref 1-4). This processing route offers technical benefits over conventional methods, including smaller size and better distribution of reinforcing phases, higher thermodynamic stability and stronger bond between the matrix and the reinforcements. However, the metallic powders and carbide forming elements normally used in these processes are rather expensive, e.g., Cr, V, and Ti. Consequently, the development of deposition strategies which employ raw materials of lower cost would be a significant achievement. With this regard, the direct reduction of oxides into carbides during the deposition process appears to offer economic benefits. The carbide forming elements of interest to this study form stable oxides, such as Cr2O3, V2O5, and, particularly, TiO2. A detailed thermodynamic study of their carbothermic reduction (Ref 5) showed that the stable oxides preferentially reduce to their respective carbides rather than to the elemental metals, with associated improvements in mechanical properties (Table 1) (Ref 6). The carbothermic reduction of TiO2 proceeds by progressive
Santiago Corujeira Gallo, Nazmul Alam, and Robert OÕDonnell, CSIRO - Process Science and Engineering, 71 Normanby Rd, Clayton, VIC 3168, Australia. Contact e-mail: Santiago.Corujeira Gallo@ csiro.au.
Journal of Thermal Spray Technology
ðEq 1Þ
The main parameters involved in this reaction are: temperature, time, and carbon ratio (C:TiO2). Most studies report carbothermic reductions of titanium oxides to occur above 1100 C and requiring several minutes or hours to achieve completion (Ref 8-11). The solidification time during hardfacing processes is considerably shorter, in the order of seconds.
Data Loading...
