X-ray Diffraction Investigation of Stainless Steel—Nitrogen Thin Films Deposited Using Reactive Sputter Deposition

Faisal I Alresheedi,James E Krzanowski

doi:10.3390/coatings10100984

Faisal I Alresheedi, James E Krzanowski

Open Access

https://doi.org/10.3390/coatings10100984

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Journal: Coatings	Publication Date: Oct 15, 2020
Citations: 4	License type: CC BY 4.0

Affiliation: University of New Hampshire, Qassim University

Abstract

An X-ray diffraction investigation was carried out on nitrogen-containing 304 stainless steel thin films deposited by reactive rf magnetron sputtering over a range of substrate temperature and bias levels. The resulting films contained between ~28 and 32 at.% nitrogen. X-ray analysis was carried out using both the standard Bragg-Brentano method as well as area-detector diffractometry analysis. The extent of the diffraction anomaly ((002) peak shift) was determined using a calculated parameter, denoted RB, which is based on the (111) and (002) peak positions. The normal value for RB for FCC-based structures is 0.75 but increases as the (002) peak is anomalously displaced closer to the (111) peak. In this study, the RB values for the deposited films were found to increase with substrate bias but decrease with substrate temperature (but still always >0.75). Using area detector diffractometry, we were able to measure d111/d002 values for similarly oriented grains within the films, and using these values calculate c/a ratios based on a tetragonal-structure model. These results allowed prediction of the (002)/(200) peak split for tetragonal structures. Despite predicting a reasonably accessible split (~0.6°–2.9°–2θ), no peak splitting observed, negating the tetragonal-structure hypothesis. Based on the effects of film bias/temperature on RB values, a defect-based hypothesis is more viable as an explanation for the diffraction anomaly.

Highlights

Since the initial discovery of the S-phase by Zhang and Bell [1] and Ichii et al [2], understanding the structural nature of this phase and the anomalous shift of the (200)/(400) diffraction peaks has been a challenging problem
In this study the nature of the well-known diffraction anomaly observed in samples of expanded austenite or the S-phase in nitrogen supersaturated stainless steels has been studied in sputter-deposited thin films
The use of this thin film deposition technique allows us to examine the effects of variations in the substrate temperature and bias, and films can be deposited at temperatures lower than those typically used in plasma nitriding of bulk samples

Summary

Introduction

Since the initial discovery of the S-phase by Zhang and Bell [1] and Ichii et al [2], understanding the structural nature of this phase and the anomalous shift of the (200)/(400) diffraction peaks has been a challenging problem. In the mid-to-late 1990’s much of the research was centered on the investigation of low-temperature plasma nitriding methods [3,4,5,6,7,8,9,10] and the development of surface hardening methods via a combination of nitrogen implantation and diffusion These processes generally are carried out within the temperature range of 250–400 ◦ C; at temperatures above 400, CrN forms, depleting the matrix of Cr and reducing corrosion resistance, while below 250 ◦ C nitrogen diffusion is too slow to form a surface layer of significant depth.

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