Laser-welded Samples Research Articles

Comparative study on weld characterisation and corrosion performance of laser-welded NiTinol

ABSTRACT Laser welding of NiTinol is a promising fabrication method. An understanding of the effects of laser heat input on different surface properties and corrosion resistance behaviour is needed for laser-welded sea water-flooded components of NiTinol. Here the effect of laser heat input on various physical, chemical and mechanical surface properties along with the corrosion resistance behaviour of the laser welded samples was investigated. The corrosion resistance performance of the phase-separated samples was found to be inferior to the other laser-welded samples. The top surface showed a superior corrosion resistance performance because of the recirculation of the melt pool and Ti enrichment on top surface.

Formability Prediction of Laser-Welded Stainless Steel AISI 304 and AISI 430

The effect of laser welding on the mechanical properties and the prediction of formability for austenitic stainless steel AISI 304 and ferritic steel AISI 430 when welded by a YLS-5000 fiber laser, were studied in the paper. The microstructure of the welded joint was analyzed using light microscopy. The mechanical properties were determined by static tensile testing. The forming limit diagrams were produced from notched samples at R5, R17, and R25 mm. The hardness values of the welded joint and the base material were determined using the Vickers method. Samples made of AISI 430 showed that the formability suffered due to laser welding. Longitudinal coarse ferrite grains were observed in the microstructure of the AISI 430 weld metal. The coarse-grained structure of the welded joint and the continuous interface along the centerline caused the failure of the AISI 430 laser-welded samples at significantly lower actual stress and strain values than were required to break the base material. No significant changes in the formability were observed in the AISI 304 samples after laser welding. The growth of dendrites was observed in the microstructure of the AISI 304 welded joint in a direction towards the centerline of the welded joint. A comparison of the experimentally determined FLD0 values and the values calculated from predictive equations showed that a better agreement was achieved for uniform elongation than for the strain hardening exponent. The manufacturability and economic efficiency of selected parts of an exhaust system by hydromechanical drawing were evaluated on the basis of the process capability index Cpk.

Effect of heat input and post-weld heat treatment on surface, texture, microstructure, and mechanical properties of dissimilar laser beam welded AISI 2507 super duplex to AISI 904L super austenitic stainless steels

In this study, AISI 2507 super duplex and AISI 904L super austenitic stainless steel sheets were successfully joined using a laser welding method with two different laser powers and laser speeds. The effects of different welding heat inputs and post-weld heat treatment on the surface, texture, microstructure and mechanical properties of laser welded joints were investigated. The results obtained in this study showed that the weld metal microstructure predominantly composed of austenite phase. In addition, the occurrence of γ-austenite (dendritic), interdendritic, ferrite, and planar, coplanar, and stacking fault was observed and also Cr23C6 precipitate was formed in the microstructure with the effect of heat treatment. In the sample joined with low heat input, an increase was observed in tensile strength, yield strength and hardness compared to the samples joined using high heat input, and a decrease in impact toughness occurred. With the effect of heat treatment, a decrease was observed in tensile, yield strength and hardness and an increase was observed in ductility and toughness. In addition, there was no significant change in the bending forces of all laser-welded samples, and the bending occurred on the super austenitic stainless steel side. While the austenite grains exhibited random orientation in the non-heat-treated and heat-treated AISI 2507 base metal and weld metal, the non-heat-treated and heat-treated AISI 904L base metal showed an orientation in the [101] and [111] directions in the transverse direction, respectively. The change in the ratio of the Schmid factor and coincidence site lattice (CSL) boundaries has a significant effect on the mechanical properties. In addition, since the kernel average misorientation (KAM) values in the interdendritic, ferrite grains and grain boundaries were higher than the austenite grains, the residual stresses were found to be higher. When the γ-austenite (dendritic), interdendritic and δ-ferrite textures were examined in the 3D-orientation distribution function maps of the non-heat-treated and heat-treated base metal and weld metal, γ-fibre and α-fibre orientations were observed at high density, and recrystallisation component (112) 〈111〉 at high density and component (113)〈332〉 with high toughness at high density appeared. The γ-austenite grains in the base metal and weld metal of the non-heat-treated and heat-treated samples showed a closer Kurdjumov–Sachs (KS) orientation relationship (OR) compared to the interdendritic and δ-ferrite grains. In the γ/δ and γ/interdendritic ORs, KS OR was generally observed, while Bain OR was observed in the heat-treated super duplex base metal. ORs known in the literature were not observed in the non-heat-treated weld metal. Densities observed in the non-heat-treated and heat-treated weld metal showed that as the sputtering time increased, the O1s spectrum decreased, and the Fe 2p, Cr 2p, Ni 2p and Mo 3d spectra increased.

Effect of Laser Welding on In-Vitro Bioactivity Properties of Ti6Al4V Joints

In this study, the Ti6AI4V alloy, which is used as an implant material in the medical field, was joined with the laser welding method at different welding speeds. The bioactivity features of the Ti6AI4V alloy and its samples joined at different welding speeds were determined by immersing in a simulated body fluid (SBF) for 1, 7, 14, 21 and 28 days. The hydroxyapatite (HA) formation on the surfaces of the samples was determined by calculating the weight gain. The weight loss was calculated by removing the HA from the surface after bioactivity testing. The corrosion rates of the samples were also determined according to the weight loss. In addition, the characterization of the HA formed on the surfaces of the samples was performed. As a result of the investigations, it was determined that the increase in laser welding speed, and therefore the decrease in heat input, positively affected the bioactivity and biocorrosion features of the Ti6Al4V laser welded joints. It was determined that the particle sizes of the HAs of the laser weldments increased with lower heat inputs. It was also observed that the amount of HA nucleated on the laser-welded samples increased in accordance with the increase in the laser welding speed. The laser welded samples that were welded at higher welding speeds and therefore at lower heat inputs, exhibited better biocorrosion behaviors.

Characterization of weld seam surface and corrosion behavior of laser-beam-welded AISI 2205 duplex stainless steel in simulated body fluid

In this study, AISI 2205 duplex stainless steel was joined with laser welding. Base material and laser-welded samples were kept in simulated body fluid (SBF) for 1, 3, 7, 14, 21, and 28 days. This research investigated microstructure, hydroxyapatite (HA) structure formed on surfaces, surface topography, and corrosion properties of samples which were kept in SBF. Characterization studies were performed by using microhardness, optical microscope, macroscope, SEM–EDS, XRD, and atomic force microscope. According to results, it was found out that HA accumulation was higher on base material surface when compared to weld seam surface, and also calcium-deficient carbonate HA structure with low crystallinity was observed on all surfaces. Very low corrosion rates due to very low weight losses were detected in all samples kept in SBF. The results showed us that heat input changes had an important effect on surface roughness values (Ra), apatite morphology on weld seam surfaces, and corrosion behaviors. Overall, it is considered that laser-welded duplex stainless steel can be used as an implant material depending on surface characterization and corrosion behaviors.

Design, research and development for plasma facing components in JT-60SA

An overview of plasma facing components (PFCs) in JT-60SA is introduced, including the upper divertor, lower divertor, inboard first wall and outboard first wall. These PFCs are upgraded in four stages during a plasma experiment in JT-60SA. At stage one, only a partial inboard first wall and upper divertor are installed with graphite tiles and inertial cooling. At stage two, the remaining PFCs including the outboard first wall and lower divertor are installed, and the inboard surface is fully covered. At stage three, the vertical targets of the lower divertor are replaced with CFC monoblock targets and water cooling. At stage four, the whole carbon wall is replaced with a tungsten wall, and remote handling for the lower divertor is introduced. The research and development on major issues concerning PFCs are presented. Mock-ups of a CFC monoblock target were fabricated and it showed good heat removal of the expected maximum heat load of 15 MW m−2 without degradation of the performance. Tungsten-coated samples were fabricated on the CFC and they showed no severe damage at surface temperatures of up to 2000 °C. Laser-welded samples showed good appearance and no defects were found by RT.

Microstructural evolution and properties of laser spot-welded Zr[sbnd]Al[sbnd]Co[sbnd]Ta bulk metallic glass under various initial welding temperatures

To enhance weldability, this study used a Nd:YAG laser (which produces a faster thermal cycle) in combination with a liquid cooling device (LCD) to spot weld (Zr53Al17Co29)99Ta1 BMG. Here, an LCD was employed to provide a variety of initial welding temperatures (IWTs), with progressively lower IWTs from room temperature (RT) to -5 °C. After the welding process, the microstructure evolution (including parent material (PM), heat affected zone (HAZ), and weld fusion zone (WFZ)), glass forming ability (GFA), and mechanical property (microhardness) of the laser-welded samples were investigated.The results showed that two types of crystallines were observed in the HAZ after RT welding. The GFA indicators of the welded samples and microhardness in the HAZ were affected significantly. When the IWT decreased to 0 °C, the crystalline phase in the HAZ and WFZ were barely noticeable which resulted in a softer HAZ; the GFA indicator of the welded sample was not substantially different than that of the PM.

Corrosion of laser-welded stainless steel orthodontic wires

PurposeFabricating orthodontic appliances using laser welding has the clinical advantage of biocompatibility, because the welded joint does not require soldered alloy. The purpose of this study was to investigate the corrosion of laser-welded stainless steel wires in acidic environments. Materials and methodsLaser welding of stainless steel wires with a 0.021×0.025 in cross-section was performed at an energy output ranging from 0.5 to 1.3kW. A control sample was prepared using conventional soldering. The samples were immersed in 1% lactic acid aqueous solution for 7 days. After immersion, the concentrations of metallic ions in solution were measured using inductively coupled plasma atomic emission spectroscopy. Tensile loading tests were carried out with and without lactic acid immersion. Scanning electron microscopy was used to examine the microstructure of laser-welded samples. ResultsThe concentrations of metallic ions detected in solution for laser-welded samples were significantly lower than that for soldered sample. There was no significant difference among the mean tensile strengths with and without immersion for laser-welded samples. The penetration depth and the localized region fused by laser irradiation increased with energy output, and ductile fractures were observed in the fused region of laser-welded samples. ConclusionLaser welding of stainless steel orthodontic wires should be acceptable for clinical use, because the joints showed sufficient strength and the original structure was not significantly altered. Immersion in acidic solution had minimal effect on the mechanical performance at the joint regions, and showed minimal acceleration of metallic ion release.

Forming Limit Diagram Prediction of Tailor-Welded Blank Using Experimental and Numerical Methods

The forming limit diagram (FLD) is a useful method for characterizing the formability of sheet metals. In this article, different numerical models were used to investigate the FLD of tailor-welded blank (TWB). TWBs were CO2 laser-welded samples of interstitial-free (IF) steel sheets with difference in thickness. The results of the numerical models were compared with the experimental FLD as well as with the empirical model proposed by the North American Deep Drawing Research Group. The emphasis of this investigation is to determine the performance of these different approaches in predicting the FLD. These numerical models for FLD are: second derivative of thinning (SDT), effective strain rate (ESR), major strain rate (MSR), thickness strain rate (TSR), and thickness gradient (TG). Results of this research show necking will be happened, when the value of MSR, TSR, ESR criteria is maximum, TG ≤ 0.78 and SDT criterion has the first peak in forming process time. The value of dome height of TWB samples at failure was predicted based on the numerical models for samples with different widths. These numerical predictions were compared with the experimental results. The SDT model indicates a better agreement with experimental results in prediction of both the FLD and the limit dome height (LDH) in comparison to the other numerical models. Both numerical and experimental results show that minimum of LDH is happened in plane strain condition.

Experimental and numerical studies on the forming behavior of tailor welded steel sheets in biaxial stretch forming

Stretch forming is an important process in making complex stampings for autobody components. In the present work formability of three different types of tailor welded blanks (TWBs) in biaxial stretch forming modes has been studied by conducting limiting dome height (LDH) tests. The TWBs are laser-welded samples of low carbon and ultra low carbon steel sheets with difference in thickness, grade and surface conditions. In TWBs with difference in thickness, the LDH decreases as the thickness ratio increases and the thickness of the thinner side is also crucial. A high thickness ratio causes two major strain peaks on thinner side and fracture takes place due to strain localization at the peak close to the pole. The weld ductility and the extent of difference in properties are the two crucial parameters for formability in TWBs with difference in properties. In both these TWBs, the fracture takes place perpendicular to the weld line and propagates towards the stronger side. Significant weld line movement occurs towards the thicker/stronger side in biaxial stretch forming. The maximum weld line movement occurs at the pole and it increases with increase in thickness ratio and becomes constant beyond a certain thickness ratio. The peak load required to deform the TWB specimens is less compared to the corresponding parent sheets. In case of TWBs with difference in thickness, as the thickness ratio increases, the peak load reduces due to decreasing punch-blank contact area.

Effects of laser welding on bond of porcelain fused cast pure titanium

To investigate the influence of the laser welding on bond of porcelain fused to cast pure titanium. Twenty cast titanium plates were divided into two groups: laser welded group and control group. The low-fusing porcelain was fused to the laser welded cast pure titanium plates at fusion zone. The bond strength of the porcelain to laser welded cast pure titanium was measured by the three-point bending test. The interface of titanium and porcelain was investigated by scanning electron microscopy (SEM) and energy depressive X-ray detector (EDX). The non-welded titanium plates were used as comparison. No significant difference of the bond strength was found between laser-welded samples [(46.85 +/- 0.76) MPa] and the controls [(41.71 +/- 0.55) MPa] (P > 0.05). The SEM displayed the interface presented similar irregularities with a predominance. The titanium diffused to low-fusing porcelain, while silicon and aluminum diffused to titanium basement. Laser welding does not affect low-fusing porcelain fused to pure titanium.

Induction heat treatment of laser welds

In this article, a new approach based on induction heat treatment of flat laser welded sheets is presented. With this new concept, the ductility of high strength steels GA260 with a thickness of 1.8 mm and CMn with a thickness of 2.13 mm is believed to be improved by prolonging the cooling time from 750 to 450 °C. Initially, a simple analytical model was used to calculate the ideal energy contributions from a CO2 high power laser source together with an induction heat source such that the temperature can be kept at 600 °C for 2.5 s. This knowledge was then used for the design of an induction coil. A number of systematic laboratory tests were then performed in order to study the effects of the coil on bead-on-plate laser welded samples. In these tests, important parameters such as coil current and distance between coil and sample were varied. Temperature measurements were made at distances of 0, 2, and 4 mm away from the virtual weld line for the induction heating process and at distances of 2 and 4 mm for the laser welding with induction heating process. For practical reasons during performance of these laboratory experiments, the induction coil was placed below the sheets, trailing the laser beam as close as possible. After welding, the samples were quality assessed according to ISO 13.919-1 and tested for hardness. The metallurgical phases are analyzed and briefly described. A comparison between purely laser welded samples and induction heat-treated laser welded samples is made. The temperature measurements show that, with the chosen mechanical setup of laser and induction coil, it is difficult to obtain a quick increase to around 300 °C, the temperatures required for efficient heat treatment with the induction coil alone. Despite this, a reduction in the hardness values of both GA260 and CMn were recorded when laser welded samples were induction heat treated. The reduction was 6%–8% for GA260 and 41%–45% for CMn, respectively. GA260 displays a ferrite structure in basic and welded form, whereas CMn, with ten times more carbon, shows a ferrite and bainite structure when laser welded. Thus, when induction heat treating, the carbon was better dispersed in the grains of CMn.

Ex vivo evaluation of human fetal membrane closure

This study compares stress and leak point pressure of human fetal membranes following closure with suture, laser welding, or a new tissue sealant, SynthaSeal. Samples of fetal membrane were bisected and repaired with suture, laser welding with albumin solders, or a tissue sealant. Representative tissue samples were assessed by histology. Anastomotic strength was evaluated by tensiometry. Additionally, leak pressure was measured after membrane samples were placed onto an infusion pump/pressure transducer, incised, and repaired as above. Membrane stress was strongest (P<0.001) for the tissue sealant group. Sutured samples were stronger than laser-welded samples. Membrane leak pressure was greatest for the tissue sealant group. The suture group demonstrated a higher leak pressure than the laser-welded group. Human fetal membranes were not suited for repair with laser welding under the conditions tested. A new tissue sealant, SynthaSeal, may provide a simple, effective method for membrane closure following fetoscopy, amniocentesis, and open fetal surgery.