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The design and construction of a planar magnetron-sputter deposition system with a beryllium chamber was accomplished to perform in-situ x-ray diffraction growth study of refractory coatings. The deposition system was set on top of a laboratory 26 x-ray diffractometer. A two-dimensional array detector was interfaced for observation of the Debye rings during growth. Integration along the 20 and directions allows fast phase and texture determination. The system was built to study effects of sputter deposition parameters on the structural properties of tantalum on steel, silicon, and glass substrates without exposing the system to atmosphere pressure. Two sputter depositions of tantalum films onto glass substrate in argon gas are reported here, one was deposited at 25-mm target-detector distance, 3.9 Pascal argon gas, and the other at 108-mm target-detector distance and 1.3 Pascal argon gas. The first film grew to 250-nm in 39 minutes at an average growth rate of 6.4-nm/minute. It consisted of 45-nm of interface layer, which showed no crystalline structure, and was most likely amorphous film. It was followed by 15-nm growth of Beta-tantalum, and then followed by 190-nm growth of alpha-tantalum. From the full-width half maximum of the plot, it was determined that the p-tantalum region was <002> textured, and the a-tantalum region was <110> textured, and grew more textured with deposition time. The second film grew to 36-nm in 22 minutes at an average growth rate of 1 .6-nm/minute. It consisted of 31-nm of layer, which showed no crystalline structure, and was most likely amorphous film. It was followed by 5-nm of surface layer of p- and a-tantalum. Ex-situ grazing incidence x-ray diffraction performed on the film surface confirmed the in-situ results. Ex-situ pole figure analysis showed <110> fiber texture in a-tantalum, and highly <002> texture in p-tantalum. more...

A prototype, rifled steel liner of 20-min inside diameter was coated with -50 to 125 micronmeter tantalum at -22.6 micronmeter/hour in krypton gas using a triode-sputter system. It was test fired with l5OO rounds for the mitigation of high-temperature and pressure wear and erosion. Growth surface analysis showed predominately alpha-phase and minimal beta-phase surface tantalum. Area detector images showed near random, slight preferred (211) crystalline orientation. X-ray diffraction revealed a thin layer of surface zinc oxide and copper firing debris on the coating surface. Compressive surface residual stress peaked near the center of the tube. Photomicrograph metallurgical examination showed general good adhesion in major parts of the bulk coatings, along with a thin layer of beta-phase nucleation, and alpha-phase or mixed alpha- and beta-phase grain growth. There was excellent behavior in soft and ductile a-tantalum areas, but cracking and disbonding occurred in beta-tantalum areas. Coating liftoff and coating loss occurred most frequently in land/groove transition and land areas, less in groove areas. Near the breech end where no coating was sputtered, the steel substrate suffered extensive cracking and environmentally-assisted heat damages. more...

An x-ray digital image plate detector was used to conduct phase and texture analyses of thin tantalum films in several seconds using a conventional, fixed copper anode, x%ay tube. This plate imaging method provides an expansion of grazing-incidence x-ray diffraction, out of the goniometer plane. The method exploits Laue flat plate geometries and "tall" Debye-Scherrer camera methods. The film studied shows 200-nm of sputter-deposited, (alpha-phase tantalum, showing <110> fiber texture grown on a silicon (100) substrate. Image plate texture information was presented, and confirmed through comparison with conventional pole figure and 20 Bragg analyses. more...

Two-dimensional image plate applications in x-ray diffraction and x-ray reflectivity characterization, using grazing-incidence geometry and radiation from a conventional x-ray tube, were explored. X-ray diffraction and x-ray reflectivity data were obtained from a conventional diffractometer with Si(Li) detector. These data complement image plate results to give more complete phase and structure information. Protective chromium coatings, electrochemically deposited onto the bore of steel cylinders, were investigated. Retained austenite content in martensitic steel was measured in simulated, inside-diameter, bore geometry. This approach demonstrates the versatility of the method for nondestructive chemical analysis and phase differentiation of interior bore surfaces in piping structures. MATLAB-based processing software was developed to facilitate quantitative image analysis, including multiple 20 scans, chi-plots, and pole figure reconstruction from multiple phi images, where chi and chi designate, respectively, specimen tilt and rotation. In x-ray reflectivity applications, 12-nm tantalum and 80-nm tantalum oxide thin films sputtered on (100)-oriented silicon wafers were investigated. Density and thin-film thickness were obtained from specular reflectivity modeling involving the periodicity of the interference fringes. Two- dimensional Kiessig interference-fringe images were analyzed and compared to conventional specular x-ray reflectivity images for the measurement of thin-film thickness and thickness uniformity over a sample. more...

X-ray reflectivity has been used to nondestructively measure the density of thin, porous, SiO2-based xerogels. Critical angle, defined by total external reflection, was measured for multiple x-ray energies to correct for sample misalignment error in me determination of the density for the films. This density was used to extrapolate the percentage of porosity, assuming a bulk SiO2 density standard. The results were compared to those obtained by Rutherford backscattering and ellipsometry techniques. more...

Manufacturing operations, such as swage autofrettage, shot peening, and overload processes, have been used to impart advantageous residual stresses to improve fatigue life in components used in high-temperature pressure vessels. Both experimental and modeling techniques depend on the geometry and processing history of the component under investigation. This report compares x-ray diffraction residual stress measurements in a swage autofrettage steel cylinder with finite element modeling results of a cylinder with a given bore expansion. The report also examines an analytical model of a cylinder under internal pressure, including both Bauschinger and strain-hardening effects. From a simple swaged cylinder to a complicated perforated cylinder and overstrained and shot-peened multiple-lug breech structure, control of residual stresses through experimental and modeling efforts is vital in the design of pressure vessels. This report discusses the role of slicing operations, surface polishing, surface roughness, and resolution effects in structures that contain high stress gradients. more...

Prototype tantalum coatings, electrochemically deposited from a molten salt onto 20-mm interior bore steel liners, exhibited superior wear and erosion behavior compared to chromium coatings. The liners were subjected to cyclic exposures of high temperature, pressure, and an aggressive chemical environment. X-ray analysis of the coatings revealed a low-hardness, randomly-oriented, body-centered-cubic, alpha-phase tantalum. Formation of tantalum oxides (predominantly Ta2O5), swaging due to the low-hardness of the coatings, a 2-micrometers layer consisting of tantalum and carbon at the tantalum/steel interface, and surface compressive residual stresses were observed. Cylindrical magnetron sputtering systems were constructed to coat 45-mm interior bore steel cylinders to protect them from wear and erosion. X-ray diffraction, scanning electron microscopy, photomicrography, and hardness analysis of several sputter-deposited tantalum specimens revealed coatings consisting of soft body-centered-cubic alpha-phase and hard tetragonal beta-phase tantalum., Presented at the 26th International Conference on Metallurgical Coatings, and Thin Films, San Diego, CA, 12-16 April 1999. Published in Surface Coatings and Technology. more...

X-ray reflectivity provides a nondestructive technique for measuring density in thin films. A conventional laboratory, Bragg-Brentano geometry diffractometer was employed to show the generalized feasibility of this technique. X-ray tubes with chromium, copper, and molybdenum targets were used to provide a large overlap of energies for density fitting. X-ray tube alignment and sample alignment were explored to find a self-consistent measurement technique. The real and complex indices for tantalum, TaOx, and porous SiO2, also known as "xerogel," were calculated and used in a reflectivity-fitting routine. The density results from multiple energies provided a self-checking method for true density extrapolation from misaligned samples. Density results for the xerogel films were compared with measurements by Rutherford backscattering spectrometry and by optical ellipsometry, and showed consistency within errors. more...

This work analyzes the unoptimized prototype triode-sputtered. 150 microns thick tantalum coatings deposited with a 2.5 microns niobium under-layer the bore of a large-diameter A723 steel cylinder. The coating was deposited for wear and erosion protection by Pacific Northwest National Laboratory. Our phase determination was based on X ray diffraction analysis, wavelength dispersive X ray fluorescence analysis, energy dispersive X ray analysis, and hardness and electrical resistivity measurements. Both X ray diffraction and radius-of-curvature methods were used to determine residual stresses. A locally developed high-resolution pole figure technique was used to perform texture analysis. The post-firing, debonded coating showed alpha-tantalum, preferred 110 orientation, high surface stresses, tantalum oxides, entrapped krypton sputtering gas, interstitial oxygen, and other impurities. The surface and subsurface pole figures revealed broadened poles and body-centered-cubic tantalum crystalline structure., Presented at 25th International Conference on Metallurgical Coatings and Thin Films, San Diego, CA., 27 Apr-1 May 98. more...

Residual stresses are believed to be responsible for the intrinsic cracks observed in electrolytic chromium coatings. The cracks directly affect the wear and erosion behavior of the coating and substrate. Crystalline orientation significantly influences the elastic-plastic properties of materials. It also affects the method by which residual stress can be determined using x-ray diffraction. For this study, we investigated texture and residual stress analysis for two low contraction (LC) chromium coating specimens and compared the results with a high contraction (HC) chromium specimen. High-resolution pole figure analysis and x-ray diffraction were used to characterize the texture in the coatings. Randomly oriented materials allow the application of the x-ray diffraction squared sin(psi) stress measurement method. For highly textured body-centered-cubic crystals, the squared sin(psi) method failed, so a Matlab matrix inversion method was used to determine residual stress. One of the LC chromium specimens exhibited near random orientation with very weak fiber texture, and the other specimen exhibited intermediate mixed <111> and <211> fiber texture. The HC chromium specimen exhibited strong predominately <111> fiber texture. A correlation between residual stress and texture was found. The HC chromium specimen with high fiber texture showed higher surface tensile stresses, while the LC chromium specimens with more randomly oriented crystallites showed lower residual stresses., Presented at SEM Spring Conference on Experimental and Applied Mechanics, Houston, Texas, June 1-3, 1998. more...

X-ray diffraction residual stress distribution analysis was performed for a swage autofrettaged, thick-walled, A723 steel compound cylinder with axial semi-circular mid-wall channels. Because of the existence of high stress gradient components in the stress distribution, the effect of spatial resolution and the x-ray beam spread function were investigated. Experimental stress measurements were compared with results from Tresca's model of a partially autofrettaged solid cylinder. Measured residual stresses were interpreted using an ABAQUS finite element model. Our experimental results verified most features of the predicted hoop stress distribution, including the high stress gradients and compressive stresses near the channel root areas. However, significantly reduced compressive stress levels were observed both near the bore and near the channel roots. An overestimate of fatigue lifetime could result if the reduction of compressive stresses observed experimentally were not taken into account. In solid autofrettaged cylinders, reduction of compressive stresses near the bore has been attributed to the Bauschinger effect. However, there is no analytical model incorporating the Bauschinger effect in the current geometry. This work demonstrated that the introduction of the semi-circular channels in a solid cylinder significantly modified the magnitude and location of stress fields. Both the bore and the channel roots are critical sites for stress concentration. Our analysis further determined that the channel roots were the most critical sites where cracks and failure should occur. Fatigue test results verified that cracking and failure occurred at the channel roots. more...

Several electrochemical deposition parameters affect grain orientations, which, in turn, affect coating quality and performance. An enhanced x-ray pole figure technique has been used to study grain distribution anisotropy in electrolytic high contraction (HC) and low contraction (LC) chromium. Temperature and current density are the most important factors controlling grain orientation. Production HC chromium deposited on steel at low temperature and low current density exhibited strong <111> fiber texture, while LC chromium deposited on steel at high temperature and high current density exhibited near random crystalline orientation. The drastic change in grain orientation on steel from strongly textured HC chromium to randomly oriented LC chromium is accompanied by marked differences in crack density, hardness, deposition rate, microstructure, thermal behavior upon heating and cooling, and improved wear and erosion performance. Laboratory LC chromium specimens that were deposited on copper plates with and without sample rotation and pulse current plating showed preferred (211) and (222) orientations. Although substrate material affects grain orientation, sample rotation and pulse current plating play a less important role. more...