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Welding-brazing method is widely used for dissimilar metals welding. However, it is becoming increasingly difficult to further improve the connection strength by controlling the formation of the transition layer. In this study, an innovative welding method referred to as adjacent welding was addressed, which greatly improved the tensile strength of Ti/Cu dissimilar joint. The strength of new joint could reach up to 89% that of copper base metal, compared to the use of a traditional welding-brazing method which strength coefficient is within the limit of 70%. In order to determine the strengthening mechanism of adjacent welding, optical microscopy, SEM, EDS and XRD were applied for the analysis of microstructure and phase structure. Furthermore, tensile strength was also tested. The results show that due to the process of remelting and reverse solidification of intermetallic compounds (IMCs) layer, a less complex and thinner IMCs layer was formed and TiCu (553 HV) with high embrittlement existing in the front of titanium substrate was changed into Ti2Cu (442 HV). Performances of joints were optimized by these changes. An interpretation module was presented for the mechanism. Keywords: Welding-brazing, Adjacent welding, Dissimilar welding joints, Intermetallic compounds

An innovative laser technique has been developed for welding 16 mm thick 304L stainless steel in the horizontal (2G) butt joint configuration. Autogenous laser welding (ALW) was applied to join the thick plate with a square groove and zero air gap, and laser welding assisted with a cold wire (LWACW) was used to fill the unfilled joint. The dimension of the square groove was optimized to achieve full penetration joint with smooth reinforcement at the back side. The wire feed process was also optimized to produce a sound weld appearance. The microstructure and mechanical properties were observed and evaluated by optical microscope, electron backscatter diffraction, microhardness measurement and tensile test. The results showed that the square groove contributed to produce a joint with deeper penetration and narrower width. The relative position of weld wire with respect to the laser spot had a great influence on the weld appearance. Sound appearance with defect-free joint was successfully produced for the 16 mm thick plate in the horizontal position. The microstructure and microhardness of the top and middle samples are different, resulting in the different tensile strength and fractured location. Keywords: Autogenous laser welding, Laser welding assisted with a cold wire, Horizontal welding position, Thick plate, Microstructure and mechanical strength

Ti2AlNb alloy is an attractive material for advanced aerospace applications. Welding of the alloy can lead to severe distortion, influencing dimensional precision of the welded workpiece and structural integration. In this study, the effect of welding parameters on the weld shape of the Ti2AlNb alloy jointed by electron beam welding was investigated. A three-dimensional thermal-elastic-plastic finite element method was developed to simulate the welding distortion. The simulation results agreed with experimental measurements very well. It showed that the developed computational approach has sufficient accuracy and can be used to predict welding distortion. Because of the low longitudinal shrinkage force, the workpiece was bent to a concave-concave shape. When welding without fixture, the bead-on-plate joint has less distortion than butt weld. Also, it was found that focus current can significantly change the weld shape, resulting in various of transverse shrinkage distributions, consequently determining transverse bending deformation. When welding heat input is kept constant, the nail-shaped weld made with a certain negative defocusing electron beam will have minimum angular distortion. Keywords: Ti2AlNb alloy, Welding distortion, Numerical simulation, Electron beam welding

The aim of the work was to produce laminated structures consisting of Ti–6Al–4V alloy and AA2519 plates and to investigate their microstructure and mechanical properties with an emphasis on the role of an additional AA1050 interlayer. Explosive welding was selected as a joining technology. The microstructure and chemical composition of the explosively joined samples were investigated. Mechanical properties were evaluated in the tensile testing and by microhardness analysis.The results demonstrated that explosive welding is an effective way to produce Ti/Al laminates. Both Ti6Al4V/AA2519 and Ti6Al4V/AA1050/AA2519 laminated plates exhibit good quality of bonding without voids and major delamination. The explosive welding produced metallurgical bonding with a nanostructured zone consisting of Al3Ti and Al2Ti phases. This zone is thicker in the joint with additional AA1050 interlayer when compared to direct AA2519/Ti6Al4V bonding. In the latter, SEM and STEM analysis reviled the presence of net-like structure in the collision zone. Advanced EDX analysis shows the enrichment of grain boundaries in copper. The formation of this structure is widely discussed. In addition, the explosive welding introduces large plastic deformation which induces the process of grain refinement in aluminium plates. Tensile testing confirms that joining section is not the weakest element of the cladded plates. Keywords: Explosive welding, Interface, Aluminium alloys, Ti6Al4V, Microstructure, Chemical analysis

To reduce longitudinal flexural deformations during the laser welding of Ti6Al4V thin plates, this paper presents a synchronous gas cooling method (SGCM) that uses liquid nitrogen-cooled argon gas with the laser source to actively control the cooling process during welding. Compared to the conventional welding, the dimension of the fusion zone (FZ) obtained with SGCM welding is the same, while the prior β grains and the acicular α′ phase for the SGCM become fine on the morphology. In the heat affected zone (HAZ), the dimension on the SGCM condition is smaller than that for the conventional welding. Furthermore, an SGCM laser welding model is developed. Simulations of the traditional laser welding process and the welding process with the SGCM show that the synchronous gas cooling affects the longitudinal flexural deformation and the longitudinal residual stress. The simulation results are verified by experiments, which show that a 71% reduction in deformation, a 21% reduction in longitudinal residual stress and a 14% reduction in longitudinal plastic strain is achieved with this method. Keywords: Laser welding, Synchronous gas cooling method, Welding deformation, Ti6Al4V titanium alloy

Laser welding of highly reflective materials, such as copper, has suffered problems such as spatter, underfill and undercut for a long time. This work analyzed the associated mechanism and suggested that appearance and integrity of laser welded copper joint could be improved by conducting the welding process at a high welding speed which is slightly below the critical welding speed for full-penetration welding at the specified laser power. The microstructure, mechanical properties and electrical conductivity of the T2 copper joint achieved under high welding speed were tested. Results show that copper joint and base material (BM) have similar electrical conductivity, the weld fusion zone (FZ) and the heat affected zone (HAZ) are softened; the tensile strength and elongation of the joint are approximately 20% and 84% below those of the BM respectively. The joint breaks near the interface between the longitudinal columnar grain structures (LC) growing along welding direction at the FZ center, and the horizontal columnar grain structures (HC) growing perpendicular to the welding direction at other area of FZ. Degradation of the mechanical properties of copper joint is attributed to the softening of the heated zone and the big angle between the growth directions of LC and HC. Keywords: 1.5-mm-thick copper, Laser welding, Defects, Microstructures, Properties

Magnesium alloys are sensitive to heat input and susceptible to grain coarsening, pores and hot cracking during welding. Cold metal transfer (CMT) with low heat input exhibits a great potential for magnesium alloy welding. In this paper, the effect of welding speed on microstructures of CMT deposited AZ31 magnesium alloy clad (when wire feed speed was 4 m/min) was investigated. A high-speed camera was used to observe the arc characteristics. And optical microscope, scanning electron microscope and energy dispersive spectrometer were employed to characterize the microstructural evolution. The results demonstrated that, the fusion zone (FZ) consisted of fine dendrite α-Mg and dispersed β-Mg17Al12. Pores were found in FZ at a higher welding speed of 14 mm/s. Grain coarsening, precipitation of β-Mg17Al12 and local melting were witnessed in the heat-affected zone (HAZ). With the decrease of welding speed, β-phase accumulated and formed the shape of band at grain boundaries, and the HAZ became more susceptible to the liquation cracks. To get a qualified cladding of AZ31 magnesium alloy, pulsed-CMT, with an optimal welding speed of 12 mm/s, was preferred. Keywords: Welding speed, Local melting, Liquation crack, Microstructure, Cold metal transfer, AZ31

In the aircraft industry double-sided laser beam welding of skin–stringer joints is an approved method for producing defect-free welds. But due to limited accessibility – as for the welding of skin–clip joints – the applicability of this method is limited. Therefore single-sided laser beam welding of T-joints becomes necessary. This also implies a reduction of the manufacturing effort. However, the main obstacle for the use of single-sided welding of T-joints is the occurrence of weld defects. An additional complexity represents the combination of dissimilar and hard-to-weld aluminium alloys – like Al–Cu and Al–Zn alloys. These alloys offer a high strength-to-density ratio, but are also associated with distinct weldability problems especially for fusion welding techniques like laser beam welding. The present study demonstrates how to overcome the weldability problems during single-sided laser beam welding of a dissimilar T-joint made of AA2024 and AA7050. For this purpose a high-power fibre laser with a large beam diameter is used. Important welding parameters are identified and adjusted for achieving defect-free welds. The obtained joints are compared to double-sided welded joints made of typical aircraft aluminium alloys. In this regard single-sided welded joints showed the expected differing weld seam appearance, but comparable mechanical properties.

This paper proposes a new welding method for joining non-ferrous metals: resistance heat assisted ultrasonic welding. Resistance heat generated by the electric Joule effect is used as an additional electrical energy source to assist ultrasonic welding process. A comparison is conducted between two dissimilar Al–Cu joints, one produced by ultrasonic welding and the other by resistance heat assisted ultrasonic welding. In the resistance heat assisted ultrasonic process, the peak power of ultrasonic vibration increases significantly. The interfacial reaction between aluminum and copper is studied as a function of the current. The thickness of the intermetallic compound layer, which is predominantly composed of CuAl2, increases with the current. At a relatively high current (1500 A), resistance heat assisted ultrasonic welding produced a dendritic solidification microstructure at the interface, due to the occurrence of a eutectic reaction, α-Al + θ → L, during the welding process. The influence of current on the mechanical properties of the joints is also discussed.

High power ultrasonic spot welding is an alternative manufacturing process which recently has been developed for joining automotive bodies. This technique is a very low energy process, forming effective welds in less than a second particularly for difficult dissimilar material combinations such as aluminium to steel joint. However, in dissimilar joint the interdiffusion and thus intermetallic formation was accelerated due to high strain rate dynamic deformation in ultrasonic spot welding which deteriorates mechanical performance. The interfacial reaction between aluminium 6111-T4 and DC04 uncoated steel has been investigated as a function of welding time. For the optimum welding time of 1.5 s under a 1.4 kN axial pressure, the intermetallic layer thickness could have reached ∼1.0 μm. Intermetallic islands were seen to nucleate across the microbonds at the interface within short welding times which spread and grow rapidly forming a continuous layer which mainly contains FeAl3 and Fe2Al5 phases. The interfacial reaction occurred in solid state even for a long welding time. Modelling was carried out with the aim of showing that the rate of interfacial reaction was over 6 times greater than the rate observed in diffusion couple using rate constants achieved from the static heat treatment condition. This confirms that deformation-induced vacancies during the thermomechanical welding process accelerates formation of intermetallic layer at the interface.

Formation of brittle intermetallic phases in addition to different thermal expansion coefficients associated with dissimilar welding leads to the formation of transverse cracks in weld metal and eventually restricts widespread applications of dissimilar joints. Therefore, joining technology should be expanded in field of dissimilar welding in order to solve its difficulties. In the present study, an experimental work with pulsed Nd:YAG laser was performed for dissimilar welding of Ti–6Al–4V and Nitinol. Autogenous welding of these two alloys resulted in joints with poor strength and ductility due to the formation of transverse cracks in the weld metal. Therefore, the chemical composition of the weld metal has to be modified in order to reduce the formation of brittle phases and eliminate subsequent cracking. In this work, this was done by insertion of a copper interlayer with a thickness of 75 μm between the base metals. The results indicated that insertion of copper interlayer has a great influence on the reduction of the amount of Ti 2 Ni brittle intermetallic phase, elimination of transverse cracks through the weld metal and eventually improvement of mechanical properties of the joints. Insertion of copper interlayer was very useful since it altered the cracked autogenous joint to a joint which could withstand a tensile stress of 300 MPa.

Ultrasonic spot welding has received significant attention during past few years due to their suitable applications in comparison to conventional fusion welding techniques. Fusion welding of dissimilar Aluminum and Stainless steel alloys is always a challenging task because of poor control on grain size and formation of undesirable brittle intermetallic compounds in the weld metal, which have deleterious effect on mechanical properties. In the past, welding of dissimilar alloys has been performed using electron beam welding, laser beam welding and friction stir spot welding, resistance spot welding, etc. However, little work has been reported on dissimilar welding of Aluminum and Stainless steel alloys using ultrasonic spot welding. The objective of the present work is to optimize ultrasonic spot welding parameters for joining 3003 Aluminum alloy with 304 Stainless steel. Welding was performed at various clamping pressures (i.e. 30, 40, 50 and 60 psi) and energy levels for investigating its effect on microstructure, mechanical properties and bond quality of the weld. Different levels of weld quality i.e. ‘under weld’, ‘good weld’ and ‘overweld’ were identified at various welding parameters using physical attributes. The weld specimens prepared with energy 125 and 150 J showed the maximum bond strength and were rated as “good” weld. It was also revealed that for a good quality weld, the maximum tensile strength is achieved once a reasonable amount of bond density and material thinning (required for the formation of metallurgical bonds) is attained.

Deep penetration laser welding of 12 mm thick stainless steel plates was conducted using a 10 kW high-power fiber laser. The effect of the processing parameters on the weld bead geometry was examined, and the microstructure and mechanical properties of the optimal joint were investigated. The results show that the focal position is a key parameter in high-power fiber laser welding of thick plates. There is a critical range of welding speed for achieving good full penetration joint. The type of top shielding gas influences the weld depth. The application of a bottom shielding gas improves the stability of the entire welding process and yields good weld appearances at both the top and bottom surfaces. The maximum tensile stress of the joint is 809 MPa. The joint fails at the base metal far from the weld seam with a typical cup–cone-shaped fracture surface. The excellent welding appearance and mechanical properties indicate that high-power fiber laser welding of a 304 stainless steel thick plate is feasible.

A systematic study on overlap welding properties of autobody galvanized steel is conducted by using the late-model fiber laser and CO 2 laser respectively. The welding joints surface formation, cross-sectional weld shape and mechanical properties of the two types of lasers are compared, and it is analyzed whether dissimilar laser sources would impact the welding quality, so as to control and optimize the craft quality of laser welding automobile body. The results show that under the test conditions, the weld fusion width presents wide at the top and narrow at the bottom and the cross-sections of overlap joints take a “Y” shape by using CO 2 laser welding, while those by using fiber laser welding have a shape like “I” which was mean the fusion widths of the upper and lower surface are almost the same. And the anti-shearing force of fiber laser welding joints was stronger due to its larger inter-sheet joint connection width. In addition, under certain conditions, the fiber laser welding could result in more uniform and finer joints, higher strength and hardness, and better mechanical properties.

The 6061-T6 Al alloy and mild steel plate with a thickness of 1 mm were successfully welded by the flat spot friction stir welding technique, which contains two steps during the entire welding process. The rotating tools with different probe lengths of 1.0, 1.3 and 1.5 mm were used in the first step, during which a conventional spot FSW was conducted above a round dent previously made on the back plate. However, sound Al/Fe welds with similar microstructure and mechanical properties can still be obtained after the second step, during which a probe-less rotating tool was used to flatten the weld surface. The sound welds have smooth surface without keyholes and other internal welding defects. No intermetallic compound layer but some areas with amorphous atomic configuration was formed along the Al/Fe joint interface due to the lower heat input. The shear tensile failure load can reach a maximum value of 3607 N and fracture through plug mode. The probe length has little effect on the weld properties, which indicates that the tool life can be significantly extended by this new spot welding technique.

Reverse dual-rotation friction stir welding (RDR-FSW) has great potential to obtain appropriate welding conditions through adjusting the independently rotating tool pin and surrounding shoulder. The welding torque exerted on the workpiece by the reversely rotating shoulder also cancels off a part of the welding torque exerted by the rotating tool pin, thus the clamping requirement for the workpiece is also reduced. In the present paper, a tool system for the RDR-FSW was designed and successfully applied to weld high strength aluminum alloy 2219-T6, and then microstructures and mechanical properties of the optimized joint were investigated to demonstrate the RDR-FSW characteristics. The weld nugget zone was characterized by the homogeneity of refined grain structures, but there was a three-phase confluction on the advancing side formed by different grain structures from three different zones. The tensile strength of the optimized joint was 328 MPa (73.7% of the base material), showing an obvious improvement when compared with the optimized joint welded by the FSW without the reversely rotating assisted shoulder. The tensile fracture occurred in the ductile fracture mode and the fracture path propagated in the weakest region where the Vickers hardness is the minimum.

The CO 2 laser overlap welding and the resistance spot welding are respectively investigated on DC56D galvanized steel used for auto body. The characteristics of the two types of welding methods are systematically analyzed in terms of the weld molding, tensile-shear performance, microstructure, hardness, and corrosion resistance of welding joint. The results show that, the fusion widths of the upper and lower surface are almost the same for the resistance welding joint, and the weld nugget is surrounded by the heat-affected zone. While the laser welding joint belongs to deep penetration welding, the weld fusion width presents wide at the top and narrow at the bottom, and the heat-affected zone is situated on both sides of the weld pool. Compared with resistance spot welding joint, laser welding joints have much more ultrafine microstructures, much smaller heat-affected zones, as well as greater resistance to deformation and corrosion. In addition, the tensile-shear performance of laser weld joints is superior to that of resistance welding joints under certain conditions.

The characteristics of laser lap welding of AZ31B magnesium alloy to Zn-coated steel were investigated. Welding was difficult when the laser beam was irradiated onto the AZ31B alloy and the processing parameters were set to obtain a keyhole welding mode. The difference in the physical properties between the two materials resulted in unstable welding process particularly when the laser beam penetrated into the steel specimen and a keyhole was formed therein. By switching to a conduction mode, the process stability was improved and successful welding could be achieved because the liquid metal film remained unbroken and the laser beam did not penetrate into the material. A 25 mm wide joint failed in tensile shear testing at loads exceeding 6000 N. This high joint strength was attributed to the formation of a 450 nm thick layer of Fe3Al intermetallic compound on the steel surface as a result of the interaction between Al from the AZ31B alloy and Fe. The presence of Zn-coating layer was essential to eliminate the negative effects of oxides on the joining process.

A new-typed joint configuration, called lap–butt joint of dissimilar aluminum alloys, consisted of a single AA6063 plate of 4 mm thick and two overlap AA5052 plates of 2 mm thick. As needed as some engineering applications, the lap–butt joint was successfully welded through the friction stir welding technique using a designed tool of W9Mo3Cr4 V with some geometric improvements. The optimum work conditions and a process map were obtained after the welding process parameter optimization experiments. The process window was built aiming to choose the suitable processing conditions to pursue the high-quality lap–butt joints. The effects of welding parameters, especially the value of pin off-set, on weld-formation, microstructures and mechanical tensile properties of the lap–butt joints of dissimilar aluminums were investigated. The parameter of pin off-set played a very important role and exerted stronger influence upon the joint quality. Three typical micro flow-patterns of plasticized materials were found in the weld-zones: circumfluence, laminar-flow and turbulent-flow. Some weld-defects and the morphologies of ‘onion rings’ were detected.

It is well known in welding of die-cast magnesium alloys that porosity is easily formed and degrades the performance of the welded joints. The porosity produced inevitably during laser deep-penetration welding has been studied through metallographic observation, gas content analyses and a high-speed X-ray transmission real-time imaging system. Porosity formation was chiefly attributed to the phenomena that the gases in the pre-existing pores in the base material were swelled to form bubbles during welding and these bubbles had few chances to escape from the weld molten pool because of the vigorous melt flows and the rapid solidification associated with high welding speeds. It was also observed that keyhole instability contributed to porosity formation by generating bubbles from a keyhole tip or a bulged keyhole. Moreover, the insertion of an extruded porosity-free alloy sheet between the die-cast alloy parts resulted in 50% reduction in the weld metal porosity.

Explosion welding (EXW) is one of the joining methods consisting of a solid state welding process in which controlled explosive detonation on the surface of a metal. During the collision, a high velocity jet is produced to remove away the impurities on the metal surfaces. Flyer plate collides with base plate resulting in a bonding at the interface of metals. The metal plates are joined at an internal point under the influence of a very high pressure and causes considerable local plastic deformation at the interface in which metallurgical bonding occurs in nature and even stronger than the parent metals. Similar and dissimilar materials can be joined by explosive welding. In this paper, after detection the theories of welding and wave formation, experimental research and numerical studies on explosive welding are reviewed for the last four decades. Also, future developments in explosive welding are predicted and criticized in an outlook.

International audience; The friction stir welding is a process which made improvement in the light construction industries. The application of this new process lies in the capacity to assemble alloys of aluminium and more obviously with alloys which are not easily weldable alloys by the traditional processes. In our study, we centered the tests on the description of the significant parameters of process FSSW (friction stir spot welding) which will be at the origin of the realization of the weld bead. This experimental approach let us notice that the shape of the tool and in particular the pawn has a great influence on the mechanical resistance of the joint of welding. This is because of the heat gradients and mechanical undergone by material during welding. The importance of these phenomena depends on the same time on the nature of material and the choice on the parameters (geometry, positioning, tool rotating, penetration depth and the force applied of the pin and the shoulder).

A new welding process, electric-resistance-heat-aided friction welding (ERHAFW), was introduced in this study. To further improve the joint quality and energy-saving, electric resistance welding was combined with the conventional continuous-drive friction welding. 21-4N (austenitic stainless steel) and 4Cr9Si2 (martensitic stainless steel) valve steel rods of 4 mm diameter were used as base metals. The results show that electric-resistance-heat-aided friction welding can be applied to join thin rods within a relatively short time, which is very difficult for conventional friction welding (FW). The microstructure of ERHAFW bonded 21-4N to 4Cr9Si2 presents non-uniform across the joint. Different structure zones are observed from the weld line to both sides, which are the weld center, thermo-mechanically affected zone (TMAZ) and heat affected zone (HAZ). These regions exhibit different structures owing to the difference in the thermophysical and mechanical properties of these two steels under the fast heating and cooling during welding. The variation of microhardness in the joint is attributed to the microstructure change. The higher microhardness is obtained in the weld center and TMAZ of 4Cr9Si2 corresponding to the presence of fine tempered martensite and carbides.

In explosive welding process, the controlled energy of explosives is used to create a metallurgical bond between two similar or dissimilar materials. This paper presents the analytical calculation for determination of weldability domain or welding window. The analytical calculations are in good agreement with experimental results. The welding conditions are tailored through parallel geometry route with different explosive loads. The study was also conducted to consider the effects of explosive loading on the bonding interface and the characterization of explosive welding experiments carried out under different conditions. Optical microscopy studies show that a transition from a smooth interface to a wavy one occurs with increase in explosive load. Scanning electron microscopy studies show that the interface was outlined by characteristic sharp transition between two materials, but local melted zones were also encountered in the front slope of waves in the interface at high explosive loads. XRD studies detected no intermetallic phases for specimen welded at low explosive load.

The continuous drive friction welding technique is usually used to join damping-tube and gland. Generally, the inner friction welding flashes at the end of damping-tube are very harmful to the assembly of damping device and the cleanness of damping liquid, these thin and natural formed inner friction welding flashes are very easy to crack, break and form a large of metal particles on the special vibrating working conditions of damping-tube, these metal particles increase wearing damage and reduce the safety coefficient of the damping-tube. It is very difficult to deal with these inner friction welding flashes of the damping-tube, especially the diameter of the damping-tube is small. To address this problem, in this article, we propose a mixed-integrated approach, which includes adjusting the size of the covering of damping-tube, designing a new structure for the tube of damping-tube, applying a controlling mould in friction welding, and optimizing the parameters of the welding technology by friction torque–time method (MT method). This approach reduces the sum of the inner welding flashes, controls the crimping direction of the friction welding flashes, and promotes the forming of the outer friction welding flashes. The macrostructure of welding flashes and friction welded are analyzed, the experimental results show that proposed mixed-integrated approach eliminates the problems of the inner friction welding flashes in the damping-tube friction welding.

Cold metal transfer (CMT) is a modified metal inert gas welding process based on short-circuiting transfer process, characterised by low heat input and no-spatter welding. The wave control characteristics and its droplet transfer process were analyzed by sensing and image method. The results show that it can realize no-spatter welding and low heat input during welding process. When welding thin sheets, it can obtain small deformation weldment. The low heat input also promotes the gap bridging ability.

Nanostructuring has been considered an effective approach to enhance the thermoelectric (TE) performance of materials by reducing their lattice thermal conductivity. In the present study, we show the influence of a process control agent (PCA) for ball milling, Stearic acid (SA), on the nano- and microstructure and thermoelectric properties of type-I clathrates in the Ba–Cu–Si system, which are promising candidates for TE applications. The SA effectively reduces cold welding and prevents particle agglomeration during ball milling. Consequently, it increases the powder yield and the milling efficiency. Smaller grain/crystallite sizes are obtained in the as-milled powders than without SA. Importantly, the SA forms nano-layers around the clathrate particles, which inhibit the grain growth during the hot pressing process used for powder compaction. Therefore, smaller grain sizes are also obtained in the hot-pressed samples. They show increased hardness and reduced thermal conductivity but also increased electrical resistivity. However, as the phonon transport is more strongly degraded than the charge transport, we observe 15% enhancement in the dimensionless thermoelectric figure of merit ZT by adding the PCA.