To suppress the tendency to form delta ferrite in weld metal (WM) of China low activation martensitic (CLAM) steel joint, a CLAM steel with revised chemical compositions was designed. Laser welding of the CLAM steel was investigated. The microstructures of the WM and heat-affected zone were analyzed. The impact toughness of the WM was evaluated by a Charpy impact test method with three V notches. The influence of temper temperature on mechanical properties was analyzed. It was found that the delta ferrite was eliminated almost completely in laser WM of CLAM steel with revised chemical compositions which has lower tendency to form delta ferrite than original chemical compositions. The joint has higher tensile strength than the parent metal. With increasing the heat input, the impact toughness of the joint is approximatively equal with that of parent metal first and then decreases obviously. Temper treatment could effectively improve mechanical property of the joint. When the temper temperature exceeds 600 °C, the impact toughness of the joint is higher than that of the parent metal.

•Influence of processing parameters on steel/copper laser welding was clarified.•Melting of copper has been suppressed effectively during welding.•Relationship between microstructures and mechanical property was clarified.•The highest tensile strength of the joint reaches to 260 MPa.The microstructures and mechanical property of stainless steel/copper laser welding were investigated by controlling the processing parameters of welding speed and laser power as well as the offset and incline angle of the laser beam in the direction of the stainless steel. The joining mode could be controllably transformed to welding–brazing from fusion welding. The welding–brazing mode joins liquid stainless steel to solid copper, whereas the fusion zone mode joins stainless steel and copper by melting and mixing both metals. Offsetting and inclining the laser beam in the direction of the stainless steel can effectively suppress the melting of the copper and ensure the joining occurs via welding–brazing. The grains of heat-affected zone (HAZ) on the side of the copper grow significantly. Liquid separation reactions induce spherical particles with copper and some bigger spherical particles with copper contained smaller spherical particles with stainless steel. The highest tensile strength of the joint reaches 260 MPa. The joint exhibited three typical modes of fracture: the interface, the heat affected zone (HAZ) and the fusion zone, depended on the processing parameters that were used. The tensile strength is weakly dependent on melting of the copper, but melting of the copper induces a decrease in the joint toughness.

Experimental investigations have been done to verify the effects of hold time during transient liquid-phase bonding on joint microstructure and mechanical properties of a nickel-based single crystal superalloy. The superalloy was bonded at 1473-1513 K for 0.25-12 h in vacuum environment. A set of parameters, 1513 K for 10 h, was determined as the optimum bonding condition. SEM results revealed that the joint without the completion of isothermal solidification is comprised of four different distinct regions, namely, rapid solidification zone (RSZ), isothermal solidification zone (ISZ), diffusion zone, and base metal. EBSD data indicated that the ISZ across the centerline of the bond has an undifferentiated crystallographic orientation being the same as the base metal. At increasing hold times at 1513 K, RSZ and also borides would disappear and result in an improvement of mechanical properties. Mechanical property tests at elevated temperatures have been done to determine the joints’ quality. High-temperature creep rupture strength (for 100 h at 1373 K) and tensile strength (at 1273 K) of the joints could both attain 90% of those of the base metal.

•The DCL LZ7C3/8YSZ coating system was prepared by the APS.•The LZ and LC in as-sprayed LZ7C3 have almost overlapping diffracted angles.•The LZ and LC in as-sprayed LZ7C3 have approximately equal diffracted intensity.•The DCL LZ7C3/8YSZ coating exhibited good thermal shock resistance.•The DCL LZ7C3/8YSZ coating has excellent thermal insulated ability.A double-ceramic-layer (DCL) thermal barrier coatings (TBC) of La2(Zr0.7Ce0.3)2O7/8YSZ (LZ7C3/8YSZ) was prepared by atmospheric plasma spraying (APS). The phase structure, composition, thermal conductivity, surface and cross-sectional morphologies, adhesion strength and thermal shock behavior of the LZ7C3/8YSZ coating were investigated. The X-ray diffraction pattern showed that the phase structures of top coat LZ7C3 was different from the powder for spraying, which consists of pyrochlore LZ and fluorite LC structures. Main peaks between LZ and LC in as-sprayed LZ7C3 have almost overlapping diffracted angles and approximately equal diffracted intensity. Thermal shock lifetime and adhesion strength of the DCL LZ7C3/8YSZ coating are enhanced significantly as compared to single LZ7C3 coating, and are very close to that of single 8YSZ coating. The mechanisms of performance improvement are considered to be effictive reduction of stress concentration between substrate and LZ7C3 coating by 8YSZ buffer effect, and the gentle thermal gradient initiated at the time of quenching in water. The DCL LZ7C3/8YSZ coating has lower thermal conductivity than 8YSZ, which was only 25% of 8YSZ bulk material and 65% of 8YSZ coating by APS.

•The laser direct butt welding of titanium alloy to stainless steel is realized.•The interfacial microstructures of the joints are confirmed.•The weldability is better when laser beam is offset toward titanium than steel.•The highest tensile strength of the joint reaches to 150 MPa.Laser butt welding of titanium alloy to stainless steel was performed. The effect of laser-beam offsetting on microstructural characteristics and fracture behavior of the joint was investigated. It was found that when the laser beam is offset toward the stainless steel side, it results in a more durable joint. The intermetallic compounds have a uniform thickness along the interface and can be divided into two layers. One consists of FeTi + α-Ti, and other consists of FeTi + Fe2Ti + Ti5Fe17Cr5. When laser beam is offset by 0 mm and 0.3 mm toward the titanium alloy side, the joints fracture spontaneously after welding. Durable joining is achieved only when the laser beam is offset by 0.6 mm toward the titanium alloy. From the top to the bottom of the joint, the thickness of intermetallic compounds continuously decreases and the following interfacial structures are found: FeAl + α-Ti/Fe2Ti + Ti5Fe17Cr5, FeAl + α-Ti/FeTi + Fe2Ti + Ti5Fe17Cr5 and FeAl + α-Ti, in that order. The tensile strength of the joint is higher when the laser beam is offset toward the stainless steel than toward the titanium alloy, the highest observed value being 150 MPa. The fracture of the joint occurs along the interface between two adjacent intermetallic layers.

The microstructures and mechanical properties of laser penetration welding joints with/without Ni-foil in an overlap steel-on-aluminum configuration were investigated. The interfacial structure between fusion zone and aluminum alloy without Ni-foil consists of FeAl/FeAl3. After the Ni-foil is added, the interfacial structure transforms into Ni1.1Al0.9/FeAl3, and the molten pool of aluminum alloy is expanded, which leads to the formation of the NiAl3 between Ni-foil and the molten pool. A banded structure composed of β(Fe, Ni)Al appears whether the joints are made with/without Ni-foil over the reaction zone. It was found that the Ni-foil enhanced tensile property of the joint, expanded usable processing parameters, and decreased microhardness of the intermetallic compounds. The enhancement of mechanical properties is attributed to the improvement of the toughness of the joint made by Ni-foil.