Volume 113, Issue 11

In the present scenario, additive manufacturing is considered to produce the functional parts in low volume. This investigation deals with the effect of process parameters viz., raster angle, orientation and type of surface on dimensional accuracy, flatness, shrinkage and surface roughness of VeroBlue RGD840 rigid opaque materials, produced by the polyjet process. A Taguchi array ( L 8 ) is used to design the experiment. Surface roughness parameters are measured by using an optical profilometer. Dimensional accuracy and flatness are measured by using coordinate measuring machines. Analysis of variance is employed to evaluate the effect of individual process parameters. An empirical model is developed to predict the dimensional accuracy, flatness and surface roughness. Results revealed that the optimum level of process parameters are different for the dimensional accuracy and flatness. A multi-objective optimization technique is employed to get the best level of process parameters. The belt level of process parameters are raster angle of 60°, orientation flat and glossy type of surface finish. The best value of surface roughness R a = 28 nm, percentage error in dimensional accuracy of 12.13 and flatness of 0.0503 mm are observed. Confirmation tests are performed at the best level of process parameters to verify the results.

The sustainability of polymer composites in real time environments can be ensured by durability studies. This paper aims to evaluate the durability of mechanical and thermal properties of graphite (G) and copper (Cu) particle-filled polypropylene (PP) composites. Three types of composites, PP/G, PP/Cu, and PP/G/Cu, were prepared by melt compounding and compression molding. The compressive strength, microhardness, and thermal properties of the composites were tested after 2 and 90 days of storage under ambient conditions. The results showed a noticeable decrease in the compressive strength of the composites, reaching ∼60–70 % compared to that of the neat PP and showed a ductile-like fracture mode. A further decrease in the strength values of ∼90 % occurred when the composites were tested after 90 days and a brittle-like fracture mode was observed. The addition of G and Cu to PP improved its microhardness and a drastic decrease also appeared after 90 days compared to that of their counterparts tested after 2 days. DSC measurements showed that the melting temperature, T m , decreased and crystallization temperature, T c , increased indicating a better ability of the fillers for nucleation in PP and obstructing its crystal growth. The degree of crystallinity, X c , of PP in the composites decreased compared to that of the neat PP and it increased when tested after 90 days compared to that tested after 2 days.

A TaC/Fe composite layer was prepared on a gray cast iron surface by using the interfacial reaction technique. The phase composition, microstructure and crystal structure of TaC/Fe composite layer were analyzed with X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The hardness and elastic modulus of TaC/Fe composite layer were examined by nano-indentation testing. The plastic deformation behavior of TaC/Fe composite layer was characterized with the index of creep stress. The results demonstrated that the intrinsic hardness and elastic modulus of TaC/Fe composite layer were 21 GPa and 413 GPa, respectively. During nano-indentation testing, the plastic deformation resistance of TaC/Fe composite layer decreased with the increase in load, while the plastic deformation resistance decreased as the loading rate rose.

In this paper, laser — tungsten inert gas (TIG) hybrid welding of TA2 titanium alloy and T2 copper alloy dissimilar joint has been performed using BCuP-2 wire as filler metal. A new welding process for TA2/T2 joining was introduced on the basis of the controlling the formation of Ti–Cu intermetallics in the joint. One process was two-pass welding involving creation of a joint with one laser weld and one TIG weld separated by remaining unmelted TA2/T2 interface. The influence of the hybrid welding process on the microstructure of the interfacial intermetallic compounds, and tensile strength of joints was investigated. The grain size of the TA2 fusion weld became larger after welding, forming acicular α martensite structure. The metallurgical combination between TIG weld and T2 base metal was good, and the TIG weld was mainly composed of α-Cu solid solution and a fine layered structure . However, a reaction layer containing α-Cu + α-Ti with an average width of about 30 μm was formed at the interface between the TIG weld and TA2 base metal, and fracture occurred along the TA2 weld and the interface of the reaction layer during tensile testing. A large number of Ti–Cu brittle compounds were avoided in joints, and the maximum tensile strength reached 610 MPa.

In this work (CoCrNi) 100− x Nb x ( x = 0–23.08 at.%) medium-entropy alloys were designed to investigate the solidification process and principle. The solid solubility of Nb in CoCrNi equiatomic MEA was discovered to be less than 0.46 at.%, and a fully eutectic structure was obtained at Co 28.9 Cr 28.9 Ni 28.9 Nb 13.3 alloy. Fcc and Laves phases are the main component phases in the (CoCrNi) 100− x Nb x alloys. With the increasing Nb content, the volume fraction of fcc decreased, accompanied by the increment of Laves phase. Based on CALPHAD and experimental results, the top-left corner of the (CoCrNi)Nb pseudo binary phase diagram was achieved. Hypoeutectic (CoCrNi) 100− x Nb x ( x < 13.3 at.%) alloys undergo the following solidification process: at first, primary dendrites with fcc structure nucleate and grow in the melt, then, eutectic reaction occurs and a mixture of Laves and fcc eutectic structure is obtained. Conversely, for hypereutectic (CoCrNi) 100− x Nb x ( x > 13.3 at.%) alloys, the primary dendrite of Laves phase form, followed by the eutectic reaction of L → fcc + Laves.

Nickel-based superalloys are widely used in thermal power, nuclear power, aerospace and other fields due to their excellent properties. Since the deformation resistance of Ni–Cr–Co superalloy is large and the forming range is narrow, the hot deformation behavior of Ni–Cr–Co superalloy was studied by hot compression experiments on a Gleeble-3800 under different deformation conditions (deformation temperature: 950–1200 °C, strain rate: 0.01–10 s −1 , and deformation: 60 %). The modified Johnson–Cook, modified Zerilli–Armstrong and strain compensated Arrhenius models were constructed based on the stress–strain curves corrected for friction and temperature. The correlation coefficient ( R ) and average absolute relative error ( AARE ) were compared to verify the accuracy of the model. The results showed that the strain compensated Arrhenius model had high accuracy, the modified Zerilli–Armstrong had high accuracy in predicting the flow behavior above 1100 °C, while the modified Johnson cook had high accuracy only under the reference conditions. Electron back-scattered diffraction analysis showed that high-angle grain boundaries formed when the low-angle grain boundaries piled up to a certain extent, which is beneficial for refining the as-cast microstructure, and the increase in strain rate was beneficial for refining the microstructure and promoting the occurrence of recrystallization.