• PDF / 2,582,996 Bytes
• 10 Pages / 606.24 x 786 pts Page_size
• 116 Downloads / 233 Views

DOWNLOAD

REPORT

---

20/1/04

2:59 PM

Page 525

Correlation of Microstructure with the Hardness and Wear Resistance of (TiC,SiC)/Ti-6AI-4V Surface Composites Fabricated by High-Energy Electron-Beam Irradiation JUN CHEOL OH, EUNSUB YUN, and SUNGHAK LEE The correlation of microstructure with the hardness and wear resistance of (TiC,SiC)/Ti-6A1-4V surface composites fabricated by high-energy electron-beam irradiation was investigated in this study. The mixtures of TiC, SiC, or TiC
SiC powders and CaF2 flux were placed on a Ti-6A1-4V substrate, and then an electron beam was irradiated on these mixtures using an electron-beam accelerator. The surface composite layers of 1.2 to 2.1 mm in thickness were formed without defects and contained a large amount (up to 66 vol pct) of precipitates such as TiC and Ti5Si3 in the martensitic matrix. This microstructural modification, including the formation of hard precipitates and a hardened matrix in the surface composite layer, improved the hardness and wear resistance. Particularly in the surface composite fabricated with TiC
SiC powders, the wear resistance was greatly enhanced to a level 25 times higher than that of the Ti alloy substrate, because 66 vol pct of TiC and Ti5Si3 was precipitated homogeneously in the hardened martensitic matrix. These findings suggested that high-energy electron-beam irradiation was useful for the development of Ti-based surface composites with improved hardness and wear properties.

I. INTRODUCTION

A Ti-6Al-4V alloy having high specific strength and stiffness and excellent corrosion resistance has been mainly used for structural and engine parts of supersonic airplanes and for armor materials.[1,2] However, its tribological properties are relatively poor because of their low resistance to plastic shearing and the low protection induced by surface oxides. Thus, studies on the development of Ti-based composites and surface treatments have been conducted to achieve Ti alloys with good surface properties.[3–8] Physical deposition techniques such as ion implantation[5] and plasma spray coating[6] and thermochemical surface treatments such as nitriding,[7] carburization, and boriding[8] have been used in order to improve the surface properties of Ti alloys. However, the former techniques are prone to interfacial separation under repeated loading conditions, and the latter techniques operated at high temperatures usually cause a torsion or twist of a substrate. To overcome these shortcomings and to improve surface properties, new surface composites have been developed by placing ceramic powders such as TiC,[9] TiB2,[10,11] TiN,[12] VC,[13] and SiC[14] on a titanium alloy substrate and irradiating them with a high-energy pulsed laser beam or electron beam. By taking advantage of ceramic qualities such as excellent resistance to heat, corrosion, and wear, surface composites having superior surface properties to titanium substrates can be fabricated.

Since fast cooling on the substrate surface can be obtained from high-energy beam irradiation methods and the input energy