Reduction of the Tensile Stress State in Laser Treated Materials

It is well known that by laser melting the wear performance of metals can be improved [ 1]. After laser treatment the surface may consist of a dendritic structure consisting of tiny cells (order of ~tm). Carbide particles may also become homogeneously dispersed. Despite these advantages, the laser treatment often results in a tensile stress in the surface layer which in the case of RCC steel (2.05 wt. % C, 11.05 wt. % Cr, 0.62 wt. % W, an

X-ray measurement of residual stresses in laser surface melted Ti-6Al-4V alloy

In this paper, we report on the residual stresses in laser surface melted Ti-6Al-4V, determined using X-ray diffraction methods. The principal result is that there is an increase in the transverse residual stress with each successive, overlapping laser track. The result can be used to explain the observation of crack formation in overlapping tracks but not necessarily in single tracks produced under identical processing conditions.

Residual stresses in the surface layer of laser-treated steels

Although laser treatment of certain metals may enhance the wear performance in general it may result equally well in large residual stresses which affect he wear performance detrimentally. Tensile stresses generated in the surface layer may lead to severe cracking of the material. This paper describes urface stress situations found after laser treatments in samples of different materials (C22, CK60 and pure Fe) with single laser tracks and in samples with multiple overlapping laser tracks. The principal results of the X-ray measurements are the large stress variations inside and outside the laser tracks. The laser treatment gives rise to both tensile and compressive r sidual stresses. The residual stresses in and around laser tracks have their origin in plastic deformation due to thermal expansion and in volume changes due to phase transforma-tions. The plastic deformation is dictated by the strength of the material and the temperature function forced upon the material by the laser treatment. The residual stress tate in multiple laser tracks is of tensile character. Each new laid laser track exerts a tensile force upon the previous laser tracks by which the compressive stresses disappear. Some annealing and/or tempering occurs, leading to a decrease inthe absolute value of the stresses. 1

X-ray stress analysis of neon implantation in laser-treated 304 stainless steel

A powerful laser beam focused on an austenitic stainless steel introduces a considerable amount of tensile stress in the first 5 µm as measured by X-ray diffraction. Microscopic analysis reveals a solidification structure 50 µm deep with a strongly oriented grain size of less than 5 µm induced by the high self-quenching rate. Subsequent implantation with a rare gas introduces a layer of pressurized gas bubbles at a depth of only 80 nm and a deformation layer as far down as 250 nm. Although the shear stress at the bubble-matrix interface transforms the metastable f.c.c. crystal structure locally into a martensitic b.c.c. phase, the actual transformed fraction is small. Mainly the implantation but also the transformation add in reducing the tensile stress by as much as 25% in total.

Mutation of the gene encoding the ROR2 tyrosine kinase causes autosomal recessive Robinow syndrome.

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Saccular Abdominal Aortic Aneurysms Patient Characteristics, Clinical Presentation, Treatment, and Outcomes in the Netherlands

Objective: The aim of this was to analyze differences between saccularshaped abdominal aortic aneurysms (SaAAAs) and fusiform abdominal aortic aneurysms (FuAAAs) regarding patient characteristics, treatment, and outcome, to advise a threshold for intervention for SaAAAs.Background: Based on the assumption that SaAAAs are more prone to rupture, guidelines suggest early elective treatment. However, little is known about the natural history of SaAAAs and the threshold for intervention is not substantiated.Methods: Observational study including primary repairs of degenerative AAAs in the Netherlands between 2016 and 2018 in which the shape was registered, registered in the Dutch Surgical Aneurysm Audit (DSAA). Patients were stratified by urgency of surgery; elective versus acute (symptomatic/ruptured). Patient characteristics, treatment, and outcome were compared between SaAAAs and FuAAAs.Results: A total of 7659 primary AAA-patients were included, 6.1% (n = 471) SaAAAs and 93.9% (n = 7188) FuAAAs. There were 5945 elective patients (6.5% SaAAA) and 1714 acute (4.8% SaAAA). Acute SaAAApatients were more often female (28.9% vs 17.2%, P = 0.007) compared with acute FuAAA-patients. SaAAAs had smaller diameters than FuAAAs, in elective (53.0mm vs 61 mm, P = 0.000) and acute (68mm vs 75 mm, P = 0.002) patients, even after adjusting for sex. In addition, 25.2% of acute SaAAA-patients presented with diameters <55mm and 8.4% <45 mm, versus 8.1% and 0.6% of acute FuAAA-patients (P = 0.000). Postoperative outcomes did not significantly differ between shapes in both elective and acute patients.Conclusions: SaAAAs become acute at smaller diameters than FuAAAs in DSAA patients. This study therefore supports the current idea that SaAAAs should be electively treated at smaller diameters than FuAAAs. The exact diameter threshold for elective treatment of SaAAAs is difficult to determine, but a diameter of 45mm seems to be an acceptable threshold.Vascular Surger