Modifications of Surface Microstructure and Properties Induced by High Current Pulsed Electron Beam (HCPEB) Treatments o
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0980-II01-11
Modifications of Surface Microstructure and Properties Induced by High Current Pulsed Electron Beam (HCPEB) Treatments of Intermetallics Thierry Grosdidier1, Jianxin Zou1,2, Gang Ji1, Kemin Zhang1, Xiangdong Zhang2, Shengzhi Hao2, and Chuang Dong2 1 LETAM, UMR CNRS 7078, Université Paul Verlaine Metz, Ile du Saulcy, Metz, 57045, France 2 State key lab. of materials modification, Dalian University of Technology, Dalian, 116024, China, People's Republic of
ABSTRACT High current pulsed electron beam (HCPEB) is a fairly new technique for surface modifications. The present contribution reviews some recent insights on the microstructure modifications encountered at the top surface of HCPEB treated (NiTi and FeAl) intermetallics. In particular, the potential of the technique for structure modifications associated with the use of the pulsed electron beam under “heating” and “melting” conditions is highlighted. The interesting surface modifications include the creation of an homogeneous protective layer under the melting mode while thermal stresses under the heating mode can induce surface hardening and stress enhanced rapid solid state alloying. INTRODUCTION The interaction of intense-pulsed energetic beams such as ion, electron and laser beams with material has been studied extensively over the past few years [1-3]. Among these pulsed beam techniques, the High Current Pulsed Electron Beam technique (HCPEB) is fairly recent. The pulsed electron irradiation induces (i) a rapid heating and cooling of the surface together with (ii) the formation of thermal stresses [4]. As a result, improved surface properties of the material, often unattainable with conventional surface treatment techniques, can be obtained fairly easily. This is particularly true for corrosion [2, 4, 5] and tribological properties [6,7]. It is well established that three different zones are usually observed in the surface depth of HCPEB treated samples. Generally present at the top surface is a zone that has been melted and subsequently solidified rapidly. It is often a few µm thick. As will be shown here, this melting can be avoided, in particular for high conductivity alloys, when the energy provided by the electron beam is not sufficiently high. Below the melted layer is found a heat affected zone (HAZ) that extends generally over a few tens of µm. Finally, a last zone, that is due to the propagation of the thermal stress wave and for which the material hardness can also be strongly affected may be present at depth far exceeding the heat-affected zone. After sufficient number of pulses (typically 15 to 20) of HCPEB treatment, this hardened zone can extend over hundreds of µm [7]. It is clear that the surface properties after HCPEB are determined by the final structurephase states generated by this thermo-mechanical treatment. This has been fairly well established for steels [2, 8] or light alloys based on Al [4, 6] and Mg [7]. However, despite the surface sensitivity of numerous intermetallics, limited information is available concerning th
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