[en] Readers should note the following error in the first sentence of Abstract for this article: “IN-38” should be “IN-738”.

[en] In the additive manufacturing of polycrystalline nickel-base superalloy Inconel-738LC (IN738LC) by laser-powder bed fusion (L-PBF), the critical issue is the formation of micro-cracks during the process. These are solidification cracks that occur at the last stage of solidification. The first part of the thesis is an extensive chemical composition analysis at high-angle and low-angle grain boundaries with solidification cracks and on those that are devoid of cracks. The second part of the thesis consists of a multi-scale residual stress study. These results are used to rationalize the contribution of solute enrichment and tensile stresses at interfaces to the solidification cracking mechanism during the L-PBF process.

[en] The main scope of this paper is to show the effects of a specific rejuvenation treatment studied for IN-38 on both the microstructure and the mechanical properties of the creep-damaged superalloy and to compare the tests results with the virgin material and with the recovery obtained through the standard heat treatment. This work will show that this rejuvenation treatment is able to recover the microstructure of creep-damaged specimens and that the creep and tensile properties of the rejuvenated alloy are even better than the virgin material for the tests performed. Moreover, it will be shown that the standard heat treatment provided for IN-738 is not able to fully recover the microstructure and that the creep properties of the superalloy during the tests have been lower than the virgin material.

[en] A study is presented on the wetting and spreading behaviour of Ag-Cu-Ti on zirconia and alumina-zirconia ceramics and on the Inconel 738. The results are discussed in terms of thermodynamic and kinetics of spreading, and on the basis of the morphological analysis, including microhardness tests, of the interfacial layers, both in the wetting couples and in the different joints

[en] In this paper, the evolution of the microstructural and performance of IN783 hightemperature bolts in service was studied. The results showed that under high-temperature service environment, with the increase of service time, the superalloy of IN783 bolt and the precipitation quantity of second phase increased. The second phase mainly existed in the form of particles and rods, which were distributed in an obvious oriented way. With the extension of service time, the strength of the alloy increased, but the hardness decreased, the plasticity and toughness decreased significantly, so it is difficult for the IN783 high-temperature bolts to reach the normal level of safe service. Therefore, the IN783 high-temperature bolts that have been in service for a long time should be strictly supervised and replaced appropriately to reduce losses.

[en] The IN738LC(Ni-base superalloy) alloy was crept undo. various creep stresses at 900 C degrees Microstructural analysis (change of γ' length and width with creep), measurement of mechanical properties(Vickers hardness) and ultrasonic nondestructive evaluation(velocity, attenuation coefficient, nonlinear parameter) were performed to investigate the effect of creep on the relationship between experimental parameters. The ultrasonic nondestructive evaluation result showed that the longitudinal ultrasonic wave velocity did not change with creep damage, while the ultrasonic attenuation coefficient increased from 6.2 dB/mm to 8.0 dB/mm. In particular, tile ultrasonic nonlinear parameter(β') increased from 0.7 tc 1.3 indicating that measurement of ultrasonic nonlinear parameter could be strong tool to evaluate the creep damage of metallic materials.

[en] This work presents a comparison of selected nickel alloys of the same condition which were treated by means of specifically chosen etching techniques. Microstructures on microscope images of wrought Alloy 617, a casting variant of Alloy 625, a polycrystalline casting alloy IN-738 LC, as well as of a monocrystalline superalloy CM 247 LC SX, respectively, are juxtaposed and evaluated. This approach allows for a comprehensive optical microscopy characterization of the characteristic microstructural features.

[en] Highlights: ► The dry sliding wear behaviour of YSZ and LZ coatings was compared. ► Empirical relationships were derived to relate the wear parameters and wear rate. ► Wear resistance of LZ coating was high due to a robust tribofilm formation. ► Both coatings provide better wear resistance up to 8% porosity compared with base metal. -- Abstract: In this paper, the friction and wear behaviours of Yttria Stabilized Zirconia (YSZ) coatings; Lanthanum Zirconate (LZ) coatings and Inconel 738 base material (BM) sliding against a sintered tungsten carbide surface were studied and compared under unlubricated conditions. Sliding experiments were performed in a pin-on-disc configuration. Further, relationships among porosity, normal load and disc speeds with respect to wear loss were derived by using the response surface methodology, and the wear mechanisms were discussed adequately. It was found that the wear resistance of the ceramic coatings gets deteriorated with the increase in the percentage volume of porosity.

[en] In Inconel 783 alloy, there are mainly two kinds of strengthening phases of β and γ’. In addition, it is found that there are other precipitated phases in the alloy’s β phase. By means of multiple testing methods, the types and functions of the precipitated phase in the β phase were determined. The results showed that the precipitated phases from β phase were nanoscale Nb and Ti carbides and a large number of white needle-like Laves phases. The former, due to its small size, which can improve the grain boundary slip resistance of the alloy, thus improves the shaping of the material. While the latter, due to its sharp shape and due to its large amount, destroys the original structure of the β phase and greatly reduces the room temperature plasticity of the alloy.

[en] Inconel 738 samples submitted to different annealing temperatures and ageing times have been investigated by small angle neutron scattering (SANS), with the aim to study precipitates phases microstructural evolution and material behaviour. The same material is a γ' (Ni₃Al, Ti) precipitation hardened nickel base superalloy adopted at high temperatures in aggressive environments, and it has found applications over a very wide range of temperature. Information on the thermal treatment effects have been obtained, in particular concerning precipitate size and volume fraction distributions. The results contribute to confirm the adopted method to a level of industrial applicability in the considered sector