Improving the Weldability of Nickel-Based Superalloy by High Frequency Vibration

The objective of this paper is to discuss the weldability of Mar-M-004 nickel-based alloy by simultaneous proceeding vibration. Three kinds of vibration modes were chosen to compare the results, including high frequency vibration, subresonant and without vibration. We used x-ray diffraction (XRD) to quantize the residual stress of each sample, also the microstructure and crystal structure were investigated by using optical microscopes. The results showed that the grain size will get refined after vibration welding, especially in high frequency vibration. From XRD and microstructure results, by using the high frequency vibration method, there has a significant effect of having lowest residual stress and lowest stress relaxation; furthermore, the formation of cracks was also inhibited and having the shortest crack length

Hot Cracking Susceptibility of 800H and 825 Nickel-Base Superalloys during Welding via Spot Varestraint Test

Hot cracking susceptibility of fillers 52 and 82 in 800H and 825 nickel-base superalloys was discussed using the Spot Varestraint test. The fillers of 52 and 82 were added into nickel-base superalloys via a gas tungsten arc welding (GTAW).Experimental results showed that the hot cracking sensitivity of the nickel-base superalloys with filler at high temperature was lower than that without filler. The hot cracking sensitivity had a slight effect when the filler 82 was added. The total length of crack was increased, the liquid-solid (L-S) two-phase range is higher so that the hot cracking susceptibility will be raised. The morphologies of cracks included the intergranular crack in the molten pool, molten pool of solidification cracking, heat-affected zone of intergranular cracks, and transgranular crack in the heat-affected zone

Evolution of Microstructure and Residual Stress under Various Vibration Modes in 304 Stainless Steel Welds

Simultaneous vibration welding of 304 stainless steel was carried out with an eccentric circulating vibrator and a magnetic telescopic vibrator at subresonant (362 Hz and 59.3 Hz) and resonant (376 Hz and 60.9 Hz) frequencies. The experimental results indicate that the temperature gradient can be increased, accelerating nucleation and causing grain refinement during this process. During simultaneous vibration welding primary δ-ferrite can be refined and the morphologies of retained δ-ferrite become discontinuous so that δ-ferrite contents decrease. The smallest content of δ-ferrite (5.5%) occurred using the eccentric circulating vibrator. The diffraction intensities decreased and the FWHM widened with both vibration and no vibration. A residual stress can obviously be increased, producing an excellent effect on stress relief at a resonant frequency. The stress relief effect with an eccentric circulating vibrator was better than that obtained using a magnetic telescopic vibrator

Residual stress measurement of yttrium barium copper oxide sol-gel films on polycrystalline magnesium oxide.

Residual stress measurement of yttrium barium copper oxide sol-gel films on polycrystalline magnesium oxide

Practical examination of the welding residual stress in view of low-carbon steel welds

The practical measurement of a welded workpiece is now feasible due to the improvement in the measuring instruments. There is a discrepancy between the theoretical and the measured welding stress profiles. In this study, stress analysis is performed on three low-carbon steel welds to investigate the reason behind the M-shaped stress profile. The welding residual stresses obtained from two different instruments show the same trend. A local high stress position is located in the tempered zone of the welding heat-affected zone. The solidification shrinkage leads to the compression of the un-melted metal near the fusion boundary and causes the discontinuous stress profile, resulting in the local high stress position in the heat-affected zone

Precipitation of Phase Using General Diffusion Equation with Comparison to Vitek Diffusion Model in Dissimilar Stainless Steels

This study performs a precipitation examination of the phase using the general diffusion equation with comparison to the Vitek model in dissimilar stainless steels during multipass welding. Experimental results demonstrate that the diffusivities (, , and ) of Cr, Ni, and Si are higher in -ferrite than (, , and ) in the phase, and that they facilitate the precipitation of the σ phase in the third pass fusion zone. The Vitek diffusion equation can be modified as follows:

Phase Transformation of δ→σ in Multipass Heat-Affected and Fusion Zones of Dissimilar Stainless Steels

The purpose of this report is to discuss the phase transformation from δ-ferrite to σ phase in various welding regions of dissimilar stainless steel welds. Experimental results indicated the grain refinement was very obvious in the second and the third pass fusion zones (304-1 and 304-2) when the welding pass increased from 1 to 3. This refining phenomenon of δ-ferrite was attributed to the recrystallization. The order of morphological development of δ-ferrite in the multipass fusion zones was as follows: massive→columnar→equiaxed. The σ phase precipitated in the third pass fusion zone (304-2) and its solidification order is L→δ+L→δ→δ+γ→δ+σ+γ with a composition of σ phase (60 wt.%Fe-35.7 wt.%Cr-4.2 wt.%Ni) of the third pass fusion zone. The precipitation mechanism of the σ phase was as a eutectoid decomposition of δ→σ+γ2

Structural and Mechanical Properties of Fluorine-Containing TaCxNy Thin Films Deposited by Reactive Magnetron Sputtering

TaN thin-film coatings are well known for their good mechanical properties, acceptable toughness, as well as good biocompatibility. However, the friction coefficient of these films is sometimes too high, or the hemocompatibility is poor. The purpose of this study is to reduce the friction coefficient and increase the hydrophobicity of TaN coatings by introducing carbon and fluorine into the coatings. This study has never been conducted by other researchers. Fluorine-containing tantalum carbonitride (i.e., F–TaCxNy) top layers were deposited on TaN/Ta interlayers by reactive sputtering with fixed nitrogen and various hexafluoroethane (C2F6) mass flow rates. During the deposition process, C2F6 gas with various mass flow rates was added. After deposition, these F–TaCxNy multi-layered films were then characterized using XRD, XPS, FTIR, FESEM, WDS, a nano-indenter, a water contact-angle measurement system, and a tribometer. The tribological tests were carried out in the environment with and without humidity. The surface energies of the films were examined with water contact-angle variation. According to structural analysis, TaN phase would transform to TaCxNy with the increase in the C2F6 mass flow rate, which would result in a decrease in the friction coefficient and an increase in hydrophobicity. The films’ hardness (H, increased at most by 20%), elastic modulus (E), and H/E ratio first increased then decreased, most likely due to the increase in relatively soft C–F bonding. According to the results obtained from tribotesting, it was found that an increase in carbon and fluorine contents in the films reduces the friction by more than 30%, and wear rate by more than 50%. More importantly, the effects of moisture on the friction coefficient can be minimized to almost nothing. In a water contact-angle study, the contact angle increased from 60° to 85° with the increase in C2F6 mass flow rates. This evidence illustrated that hemocompatibility of the TaN thin film can be significantly enhanced through the formation of Ta–C and C–Fx bonding. The chemical composition and bonding status of these films, especially the existence of C–Fx bonds, were studied by FTIR and XPS. In sum, with the increased C2F6 mass flow rate, the carbon and fluorine contents in the films increased, while the nitrogen content decreased. The structure, bonding status, and compositions varied accordingly. The tribological behaviors were significantly improved. Furthermore, by carrying out tribotesting in humid air and a dry argon environment, it was confirmed that the greater the fluorine content, the less sensitive the films would be to environment change. This is attributable to the induced lower surface energy and reduced adsorption to water vapor due to the increase in C–Fx bonds. The successfully fabricated and studied F–TaCxNy films could be applied in many areas such as artificial blood vessels, or precision components in an atmospheric or vacuum environment