Cracking Behavior of Two Kinds of Plasma Cladding Layers by Precursor Carbonization-Composition Process

In-situ synthesized two kinds of Fe-Cr-C and Fe-Cr-C-Ti layers were fabricated on the base of Q235 steel by reactive plasma cladding process using composite powder prepared by precursor carbonization-composition process as raw materials. The composite powder is composed of ferrotitanium, chromium, iron and precursor sucrose. Microstructure of the layer was observed by scanning electron microscope (SEM). The phases in the layer were determined by X-ray diffraction (XRD). Results indicate that the Fe-Cr-C layer consists of primary (Cr,Fe)7C3 carbide, chrysanthemum-shaped eutectic (Cr,Fe)7C3 carbide and eutectic austenite. The cracks in Fe-Cr-C layer might originate at the interface of the layer and the base material as well as at the pores or edges of the layer. These cracks expand along primary (Cr,Fe)7C3 grain boundaries in a crystalline form. Because the grains of primary (Cr,Fe)7C3 are fiber-shaped and the fiber direction are perpendicular to the surface of the layer, so the cracks expand perpendicularly throughout of the Fe-Cr-C layer. The Ti addition into Fe-Cr-C plays an important role in synthesizing TiC and austenite, reducing primary (Cr,Fe)7C3 and improving the microstructure of eutectic (Cr,Fe)7C3. Therefore, Fe-Cr-C-Ti has good performance in toughness and crack-resistance.