[en] Laser welding is potentially advantageous because of its flexibility and the reduced amount of material affected by the weld. Lasers do not require a vacuum (as do electron beam welders) and the welds they produce high depth-to-width ratios. Scoping with a small pulsed 50 J YAG laser indicated that lasers could produce successful welds in vanadium alloy (V-5%Cr-5%Ti) sheet (1 mm thick) when the fusion zone was isolated from air. The pulsed laser required an isolating chamber filled with inert gas to produce welds that did not contain cracks and showed only minor hardness increases. Following the initial scoping tests, a series of tests were preformed with a 6 kW continuous CO₂ laser. Successful bead-on-plate welds were made on V-4%Cr-4%Ti and V-5%Cr-5%Ti alloys to depths of about 4 mm with this laser

[en] A major problem in the understanding of the airborne transport of radioactivity in mines is the lack of detailed knowledge of mass transfer to and fluid flow over rough walls under fully developed turbulent flow conditions. This paper will report the progress on a project that is designed to obtain that information

[en] The purpose of this investigation was to determine if a stenosis of a coronary artery located proximally caused greater deterioration of left ventricular function than a stenosis of a similar magnitude located more distally in the artery. Twenty-six patients with isolated left anterior descending coronary artery (LAD) lesions documented by cardiac catheterization were studied by radionuclide angiocardiography (RNA) at rest and during exercise on a bicycle ergometer. Thirteen patients (nine males and four females) had a proximal lesion of the LAD averaging 9.1 +/- 11% of the diameter of the lumen (group 1) and 13 patients (eight males and five females) had a distal lesion averaging 88 +/- 12% of the lumen (group 2). The mean age of group 1 was 49 +/- 9 years and the mean age of group 2 was 48 +/- 9 years. The findings indicate that a stenotic lesion located at a more proximal level of the coronary arterial system reduces blood flow in a larger area of myocardium, resulting in a more pronounced ischemic response to exercise than a similar lesion located more distally

[en] Laser welding is potentially advantageous because of its flexibility and the reduced amount of material affected by the weld. Bead-on-plate and butt welds were previously performed to depths of about 4 mm with a 6-kW CO₂ laser on V-4%Cr-4%Ti and V-5%Cr-5%Ti alloys. These welds were made at a speed of 0.042 m/s using argon purging at a flow rate of 2.8 m³/s. The purge was distributed with a diffuser nozzle aimed just behind the laser beam during the welding operation. The fusion zones of welds made under these conditions consisted of very fine, needle-shaped grains and were also harder than the bulk metal (230-270 dph, compared to ∼180 dph for the bulk metal). A limited number of impact tests showed that the as-welded ductile-brittle transition temperatures (DBTT) was above room temperature, but heat treatment at 1000 degrees C for 1 h in vacuum reduced the DBTT to <-25 degrees C. Activities during this reporting period focused on improvements in the purging system and determination of the effect of welding speed on welds. A 2-kW continuous YAG laser at Lumonics Corp. in Livonia, MI, was used to make 34 test welds for this study

[en] A systematic study has been in progress at Argonne National Laboratory to examine the use of YaG or CO₂ lasers to weld sheet materials of V-Cr-Ti alloys and to characterize the microstructural and mechanical properties of the laser-welded materials. In addition, several postwelding heat treatments are being applied to the welded samples to evaluate their benefits, if any, to the structure and properties of the weldments. Hardness measurements are made across the welded regions of different samples to evaluate differences in the characteristics of various weldments. Several weldments were used to fabricate specimens for four-point bend tests. Several additional weldments were made with a YaG laser; here, the emphasis was on determining the optimal weld parameters to achieve deep penetration in the welds. A preliminary assessment was then made of the weldments on the basis of microstructure, hardness profiles, and defects

[en] A systematic study has been initiated to examine the use of lasers to weld sheet materials of V-Cr-Ti alloys and to characterize the microstructural and mechanical properties of the laser-welded materials. In addition, several post-welding heat treatments are being applied to the welded samples to evaluate their benefits, if any, to the structure and properties of the weldments. Hardness measurements are made across the welded regions of different samples to evaluate differences in the characteristics of various weldments

[en] Mechanical properties and microstructural characteristics of laser and electron-beam (EB) welds of a 500-kg heat of V-4Cr-4Ti were investigated in as-welded condition and after postwelding heat treatment (PWHT) by impact testing, microhardness measurement, optical microscopy, X-ray diffraction, and transmission electron microscopy (TEM). Ductile-brittle-transition temperatures (DBTTs) of the laser and electron-beam welds were significantly higher than that of the base metal. However, excellent impact properties could be restored in both types of welds by postwelding annealing at 1000 C for 1 h in vacuum. Analysis by TEM revealed that annealed weld zones were characterized by extensive networks of fine V(C.O.N) precipitates, which clean away O, C, and N interstitials from the grain matrices. This process is accompanied by simultaneous annealing-out of the dense dislocations present in the weld zone. This finding could be useful in identifying an optimal welding procedure by controlling and adjusting the cooling rate of the weld zone by an innovative method to maximize the precipitation of V(C,O,N). (orig.)

[en] The deposition rate of submicron particles from turbulent gas streams was investigated and found to be consistent with a correlation derived by Kader and Yaglom. The data include deposition measurements of particles having diameters ranging from 0.041 to 0.2 μm and roughness configurations varying from a spacing to height ratio, P/K of 2 to 25. The results indicate that the correlation developed by Kader and Yaglom can be used to predict submicron particle deposition over a wide range of roughness geometries. Their approach can also be extended to estimate deposition rates of molecules and molecular clusters on rough surfaces so that the entire range of rough wall deposition from molecular size to submicron particles can be estimated with good precision. (author)

[en] The performance of a fiber-optic laser beam delivery system strongly depends on the fiber and the optics used to image the fiber face on the workpiece. We have compared off-the-shelf homogenous (BK7) and GRADIUM (axial-gradient) singlets to determine what improvement the GRADIUM offers in practice to the typical laser user. The realized benefit for this application, although significant, is much smaller than would be realized by a conventional imaging application. The figure of merit for laser-based materials processing is the 86% energy-enclosure radius, which is not directly supported by commerical ray-tracing software. Therefore empirical rules of thumb are presented to understand when GRADIUM (or any other well-corrected optics) will yield meaningful improvement to the beam delivery system. copyright 1997 Optical Society of America

[en] This study examines the application of laser ablation to the characterization and decontamination of painted and unpainted concrete and metal surfaces that are typical of many facilities within the US Department of Energy complex. The utility of this promising technology is reviewed and the essential requirements for efficient ablation extracted. Recent data obtained on the ablation of painted steel surfaces and concrete are presented. The affects of beam irradiance, ablation speed and efficiency, and characteristics of the aerosol effluent are discussed. Characterization of the ablated components of the surface offers the ability of concurrent determination of the level of contamination. This concept can be applied online where the ablation endpoint can be determined. A conceptual system for the characterization and decontamination of surfaces is proposed