Wear Behavior and Structural Characterization of a Nitrogen Implanted Ti6Al4V Alloy at Different Temperatures
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WEAR BEHAVIOR AND STRUCTURAL CHARACTERIZATION Ti6Al4V ALLOY AT DIFFERENT TEMPERATURES
R.
MARTINELLA*,
*C.I.S.E.,
G. CHEVALLARD*,
P.O.B.
12081,
OF A NITROGEN IMPLANTED
AND C. TOSELLO**
Milan Italy; **I.R.S.T.,
Trento,
Italy
ABSTPACT Mechanically polished Ti6Al4V samples were implanted 2 with 100 key nitrogen ions to a fluence of 5-1017 ions/cm at two different bulk tenneratures: 370 oC and 470 °C. Wear tests were carried out with a reciprocating slidina tribotester. Structural modifications and wear morphologies were studied by TEM and SEM. 370 °C implanted sample showed the same wear behavior as unimolanted ones, while 470 °C implanted sample showed better wear resistance because of a TiN hardened layer. Correlations- between microstructural modifications, wear behavior and mechanisms are reported: results agree with the delamination theory. Comparison with ion- and qas-nitrided samples are presented.
1. INTRODUCTION Titanium alloys, which are widely used because of their high corrosion resistance, mechanical properties and low density, show a very poor wear resistance. Among different anti-wear surface treatments (carburizing, nitriding,hard coating,etc.) ion imnlantation is interesting because no mechanical,dimensional and strong surface finishing modification is produced [i] Works regarding ion implantation of Ti and its alloys [2-5] give preferential attention to increased hardness and chemical and/or structural modifications; only few wear tests are reported, but without correlation between microstructural modifications, wear behavior and mechanisms, where there is still a lack of understanding. Shepard et al.[5] reported a wear mechanism, based on the delamination theory, capable of a comprehensive interpretation of wear and structural results, but without any detailed study of microstructural modifications. Preliminary results on wear behavior and structural modifications of Ti6Al4V samples, nitrogen implanted at two temperatures are reported and are internreted in terms of the delamination theory. Some results obtained on gas- and ion-nitrided samples are also reported for comparison.
2. EXPERIMENTAL 2.1. Materials 2
Ti6Al4V bars (HV5 0 x 420 kg/mm ) and 10% Co H.S. tool steel (HV5 0 n 850 2 kg/mm ) sliders were used. Surface for wear tests were optically lapped (Ra on Ti6Al4V n O.O1 sm). 2.2.
Surface treatments
At IPST in Trento 100 keV nitrogen ions were implanted on cleaned 2 2 Ti6Al4V bars at doses of 5.1017 ions/cm with nu80 VA/cm current density in
Mat.
Res.
Soc. Symp.
Proc. Vol. 27 (1984)
Published by Elsevier Science Publishing Co.,
Inc.
712
4 'x. 10Pa vacuum. Different thermal insulation allowed US to reach two different bulk regime temperatures: N 370 OC and u 470 fC, measured at 1.5 mm under the implanted surface with a Cr-Al thermocouple. For comparison some Ti6Al4V samples were ion- and N2 gas-nitrided at 850 0C for 10 and 20 hours, respectively.
2.3. Wear tests A reciprocating slider on bar tribotester equipped with a proximity transducer was used (fig. 1). Tests wer
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