DEPTH PROFILING AND MICROANALYSIS OF HYDROGEN IN TITANIUM

Abstract

Hydrogen has dramatic effects on the properties of metals and the quantity and distribution of hydrogen in titanium is an important consideration in many applications. This report describes methods of chemical analysis, depth profiling, microanalysis and surface analysis useful in studying the distribution and state of hydrogen in titanium. RESULTS AND DISCUSSION Bulk Chemical Analyses If sufficient hydrogen exposure has occurred, a brittle bulk hydride layer will form (Figure 1). It can be delaminated from the substrate and bulk analyzed for Ti by neutron activation analyses and for H by combustion analysis (950°C in purified oxygen). The H/Ti weight ratio can be used to identify the hydride based on stoichiometry. The H/Ti ratio measured herein of 0.0405 was in good accord with the results of x-ray diffraction which identified the hydride as TiH (H/Ti = 0.040). Depth Profiling Chemical etching of polished cross-sections readily, but not specifically, reveals a region of bulk hydride overlaying a two phase region consisting of acicular titanium hydride and a Ti (Figure 1). At low hydrogen exposures the acicular hydride appearance is similar to that of nitride? and mechanical twins. The thickness of the bulk hydride can be estimated by measuring the impact strength of the hydrided Ti because the Charpy impact strength shows an approximate loss of 0.9 ft. lbs. per Mn> of bulk hydride thickness up to about 200 (jm. Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19842167 C2-722 JOURNAL DE PHYSIQUE Figure 1 Polished and etched cross-sections of titanium after different hydrogen exposures. A shows about 350 pm of bulk hydride while B shows nil bulk hydride. The marker represents 250 pm. Krolls etchant: 2 ml HF, 10 ml HN03, 30 ml lactic acid; swab for 20 seconds. Secondary ion mass spectrometry (SIYS) performed in an ion probe is exceptionally useful for studying H in metals (1). Figure 2 is a SIMS profile across the Ti section shown in Figure 1A. The H+ counts clearly delineate the regions of bulk hydride, hydride + a Ti and finally a region of dissolved hydrogen which extends for hundreds of pm. The 5 1 ~ i ~ + profile was similar. The depth of hydrogen penetration was in accord with that predicted by bulk diffusion. The detection limit in this analysis + was 1 at.% H. Figure 3 is a H image of the interfacial region between bulk hydride and hydride + a Ti. l i t cwne an Atom % Hydrogen bulk hydrlde Tun2 + a T I no vnrtble hydrlde preclpttatlon 67 Conditions: IMS 3M) 30 pm analysis diameter 5.5 kV 0;