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Purpose This paper aims to investigate the effect of aluminum addition on the microstructure and mechanical properties of Mg-8Gd-4Y-1Zn alloy. Design/methodology/approach Mg-8Gd-4Y-1Zn-xAl (x = 0, 0.5, 1.0, 1.5, 2.0 Wt.%) alloys were prepared by the conventional gravity casting technology, and then microstructures, phase composition and mechanical properties were investigated by material characterization method, systematically. Findings Results show that the as-cast microstructure of Mg-8Gd-4Y-1Zn alloy mainly consists of a-Mg matrix as well as Mg12REZn (18 R LPSO structure), and island-like Mg3(RE, Zn) phase is distributed at the grain boundary. The addition of a small amount of Al (0.5 Wt.%) can decrease the content of island-like Mg3(RE, Zn) phase, but significantly increase the content of long-period stacking ordered (LPSO) structure, resulting in the improvement of both tensile strength and elongation of Mg-8Gd-4Y-1Zn alloy. However, the addition of excessive Al will consume Re element and decrease the amount of LPSO structure, leading to the decrease of tensile properties. When the content of Al is 0.5 Wt.%, the tensile strength and elongation are 225 MPa and 9.0% of Mg-8Gd-4Y-1Zn alloy, which are 14% and 29% higher than that of Mg-8Gd-4Y-1Zn alloy, respectively. Originality/value Adding aluminum to Mg-8Gd-4Y-1Zn alloy strengthens its mechanical properties. And the effect of Al content on the alloy strengthening. The formation mechanism of LPSO structure with different aluminum content was revealed.

Laser thermography is a novel non-destructive testing method enabling the detections of defects on vertical surfaces (e.g., cracks) and those on parallel surfaces (e.g., delaminations). The thermal response of defects near the surface of the specimen in the temperature field is the basis for defect detection work; however, the thermal response characteristics of defects under direct laser irradiation have not been systematically investigated. In this paper, we investigated the thermal response characteristics of five materials under long-pulsed laser excitations: copper, 45 steel, aluminum alloy, carbon fiber reinforced polymer plate, and ceramic resin composite coating. These specimens exhibited significantly different thermal conductivities. An important characterization parameter, characteristic temperature, was found, which can characterize the difference in thermal conductivity of different specimens. The surface of the 45 steel was coated with 3Cr13 coating, and cracks on the coating surfaces generated significantly different thermal response characteristics. The findings of this study illustrated the feasibility of long-pulsed laser thermography for demonstrating the heat entrapment effect due to cracks and provide a method for defect detection.

Intrinsic structural limitations of plasma-spray TiO2 coating deteriorate its wear resistance. Herein, CNTs are incorporated in the coating to assess their effects on the microstructure and tribological properties. Structurally, degradation degree of CNTs in TiO2 matrix during plasma spraying was revealed by Raman spectroscopy. And high resolution transmission electron microscopy manifested that TiO2/CNT interface was well bonded along with presence of notable interfacial carbothermic product TinO2n-1 at atomic scale. The phenomenon indicates a beneficial effect for transferring stress from matrix to CNTs effectively. Then, the influence of CNTs on coating’s friction behavior was investigated by zirconia ball-on-disk tribometer under dry-sliding condition. As compared to TiO2 coating, the nanocomposite coating exhibited a moderate decrease in friction coefficient and an enormous reduction (∼93.6%) in wear volume. The remarkable advance in tribological properties of the reinforced coating can be attributed to four kinds of frictional effects of CNTs: tribo-reorientation, tribo-protruding, tribo-film and tribo-degradation.

Pb(Mg 1/3 Nb 2/3 )O 3 -Pb(Z r0.48 Ti 0.52 )O 3 coatings were obtained by supersonic plasma spray. With subsequent heat treatment, compact structure and typical tetragonal phase were obtained, and therefore dielectric performance (e r ≈ 915 at ambient temperature) have been significantly improved. The reason for successfully promote the properties is attributed the elimination of defects, amorphous and pyrochlore phase. Detail analyses were conducted on the variation of defects (pores and micro-cracks) and phase (amorphous, pyrochlore) of coatings after treated at elevated temperature. With the analyses, the existence of pyrochlore phase and ZrO 2 are attributed to the incongruent melting behavior. Inhibition of grain growth is attributed to the accumulation of ZrO 2 in the grain boundary. The results also suggest the subsequent change from pseudocubic to tetragonal at elevated temperature.

This article reports that the uniformity of the alloy steel 20Cr2Ni4A is improved by using pulsed magnetic treatment. The pulsed magnetic field with 1, 4 and 9T was applied on the tempered samples. Meanwhile the microstructures were characterized using transmission electron microscopy and magnetic force microscopy, and mechanical properties tested to verify the effect of the proposed process. It shows the contact fatigue life of alloy steel increases by 42.11% after magnetic treatment. Range of residual stresses narrows down along with rise of magnetic induction strength. The microstructures of dislocations, precipitates, and magnetic domains become more uniform under pulsed magnetic field. Besides, dislocations and precipitates were observed to transit from intergranular agglomeration to intracrystalline distribution. The energy of the external magnetic field promotes the dislocation slip and reduces high dislocation density on grain boundaries, which results in a decrease of residual stress.

It has been a challenging task to estimate the size of thermal barrier coating disbonds by pulsed thermography, because thermal images are naturally blurred by lateral heat diffusion around the edge of defect. In the present work the first derivative images were employed to weaken the effect of lateral thermal diffusion, in a similar way as for Full Width at Half Maximum (FWHM) based on thermal images. Theoretical analysis introduced the correspondence of thermal profile and the first derivative profile along diameter of an in-plane defect, it’s found that half maximum points of two side dips in the first derivative profile is much closer to the real defect edge than the half maximum points of positive peak in temperature profile. Experimental results suggested that FWHM-1st based on the first derivative images generated more precise estimated values of coating disbonds than FWHM did. In addition, Evolution of FWHM and FWHM-1st in cooling process also revealed that it’s the early images in regular regime of transient heat conduction give more precise estimation of disbonding size instead of traditionally considered early images just at the final instant of optical pulse.

The service condition determines the Rolling Contact Fatigue(RCF) failure mechanism and lifetime under ascertain material structure integrity parameter of thermal spray coating. The available literature on the RCF testing of thermal spray coatings under various condition services is considerable; it is generally difficult to synthesize all of the result to obtain a comprehensive understanding of the parameters which has a great effect on a thermal spray coating’s resistance of RCF. The effects of service conditions(lubrication states, contact stresses, revolve speed, and slip ratio) on the changing of thermal spray coatings’ contact fatigue lifetime is introduced systematically. The effects of different service condition on RCF failure mechanism of thermal spray coating from the change of material structure integrity are also summarized. Moreover, In order to enhance the RCF performance, the parameter optimal design formula of service condition and material structure integrity is proposed based on the effect of service condition on thermal spray coatings’ contact fatigue lifetime and RCF failure mechanism. The shortage of available literature and the forecast focus in future researches are discussed based on available research. The explicit result of RCF lifetime law and parameter optimal design formula in term of lubrication states, contact stresses, revolve speed, and slip ratio, is significant to improve the RCF performance on the engineering application.

It has always been a challenge for most non-destructive testing (NDT) methods to discriminate the crack defects in substrate beneath sprayed coatings, owing to the interruption to testing signal by coating cracks. Ultrasonic infrared thermography (UIT) was employed to solve this problem in the current work. Coating crack and substrate crack were regarded as heat sources lying at different depth when excited by ultrasonic vibration. Coherent interference of thermal waves emitted from coating crack and substrate crack was introduced theoretically, and phase deviation (PD) of mixed thermal wave on surface was draw out as the discriminating feature for the deeper heat source, scilicet the substrate crack. Finite element modelling (FEM) results suggested that PD was more intensive in lower frequency range than that in higher frequency range. The proposed PD feature was validated experimentally with a plate specimen in which coating crack and substrate crack generated artificially under controlled monaxial cycle tensile load, experimental results were in qualitative agreement with FEM results. In addition, both FEM results and experimental results indicated that PD was insensitive to the heating intensity of crack defects under ultrasonic excitation, which was deemed to be a main unrepeatable parameter in UIT.

Molybdenum zirconium titanium (Mo-Zr-Ti) and molybdenum zirconium titanium rhenium (Mo-Zr-Ti-Re) composite coatings were deposited by supersonic plasma spraying technology. Scanning electron microscopy (SEM), energy dispersive microanalysis (EDS), transmission electron microscope (TEM) and indentation test were used to investigate the microstructure, phase composition and mechanical properties of the coatings. SEM and EDS results showed that the Mo-Zr-Ti-Re coating was composed of bright and grey areas corresponding to Re-rich and Re-poor microstructure areas, respectively. TEM indicated that the Mo-Re alloy phase and Ti-rich areas were formed in the composite coating. Indentation experiments found that radial and edge cracks were extended at the indentation of the two kinds of coatings. The hardness, elastic modulus, and fracture toughness of the Mo-Zr-Ti-Re coating were improved by 21%, 9%, and 30%, respectively, in comparison with those of the Mo-Zr-Ti coating. The observed toughening mechanisms were crack branches and crack deflection, which can effectively inhibit crack propagation.