Recent development in friction stir processing of aluminum alloys: Microstructure evolution, mechanical properties, wear and corrosion behaviors

In this paper, the effect of mechanical vibration with reinforcement particles namely Silicon Carbide (SiC) on microstructure, mechanical properties, wear, and corrosion behaviors of aluminum alloy surface composites fabricated via friction stir processing (FSP) was investigated. The method was entitled friction stir vibration process (FSVP). The results revealed that recrystallized fine grains formed in all processing samples as a result of dynamic recovery and recrystallization, while samples processed in friction stir vibration processing resulted in better grain refinement in the stir zone than in conventional friction stir processing. Compared to conventional friction stir processing, in friction stir vibration processing, the hardness and tensile strength increased due to microstructure modification and better reinforcing distribution. From corrosion analysis, the corrosion resistance of the friction stir vibration processed samples showed a significant increase compared to the friction stir processed specimens. The wear results indicated that the wear resistance of friction stir vibration processed specimens is higher than friction stir processed specimens due to the development of smaller grains and a more homogenous distribution of the strengthening particles as the vibration is applied.

MODELING THE ACCUMULATION OF DAMAGES AND THE FAILURE OF CERAMIC COMPOSITES Al2O3-ZrO2, OBTAINED BY ADDITIVE TECHNOLOGIES, UNDER HIGH-SPEED LOADING

Functional ceramic composite materials are widely used in industry due to their high strength, hardness, high operating temperature, and chemical inertness. Among the most famous types of functional ceramics are the ceramic composites based on the Al2O3-20% ZrO2 system. In this work, the effect of the loading rate on the crack resistance is studied as well as the effect of the crack resistance of ceramic composites Al2O3-20% t-ZrO2 with a mass content of submicron tZrO2 particles on the high-speed compression of model specimens in shock waves and on the high-speed tension in the region of interaction of unloading waves. It is established that nonlinear effects of the mechanical behavior of ceramic composites ZrO2-Al2O3 with a transformationhardened matrix obtained by additive technologies are manifested at shock loading amplitudes close to or exceeding the Hugoniot elastic limit. Nonlinear effects under intense dynamic impacts on the considered composites are associated with the processes of self-organization of deformation regimes at a mesoscopic level, as well as with the occurrence of martensitic phase transformations in the matrix volumes, which are adjacent to strengthening particles. The modeling approach presented in this work can be used to determine the dynamic characteristics of ceramic composites up to shock loads of 1000 m/s.

Microstructure and Damage Evolution During Thermal Cycling of Sn-Ag-Cu Solders Containing Antimony

Antimony is attracting interest as an addition to Pb-free solders to improve thermal cycling performance in harsher conditions. Here, we investigate microstructure evolution and failure in harsh accelerated thermal cycling (ATC) of a Sn-3.8Ag-0.9Cu solder with 5.5 wt.% antimony as the major addition in two ball grid array (BGA) packages. SbSn particles are shown to precipitate on both Cu6Sn5 and as cuboids in β-Sn, with reproducible orientation relationships and a good lattice match. Similar to Sn-Ag-Cu solders, the microstructure and damage evolution were generally localised in the β-Sn near the component side where localised β-Sn misorientations and subgrains, accelerated SbSn and Ag3Sn particle coarsening, and β-Sn recrystallisation occurred. Cracks grew along the network of recrystallised grain boundaries to failure. The improved ATC performance is mostly attributed to SbSn solid-state precipitation within β-Sn dendrites, which supplements the Ag3Sn that formed in a eutectic reaction between β-Sn dendrites, providing populations of strengthening particles in both the dendritic and eutectic β-Sn.

Simulation of the Dynamic Behaviour of the ZTA Composites Obtained by Additive Technologies

This paper presents a physical and mathematical model that has been developed in the framework of the approach used in the computational mechanics of materials. The model is designed to enable the study of the patterns of deformation and fracture of ceramic composites with a transformation-hardened matrix that are obtained by additive technologies at the mesoscopic and macroscopic levels under intense dynamic loading. The influence of the loading rate on the formation of the fracture and energy dissipation fronts for composite materials, based on the Al2O3 20%ZrO2 system, is shown. Nonlinear effects under intense dynamic loading in the considered composites are associated with the processes of self-organization of structural fragments at the mesoscopic level, as well as the occurrence of martensitic phase transformations in matrix volumes adjacent to the strengthening particles.

Pure Aluminum Structure and Mechanical Properties Modified by Al2O3 Nanoparticles and Ultrasonic Treatment

This paper examines dispersion hardened alloys based on commercial-purity aluminum obtained by permanent mold casting with the addition of aluminum oxide nanoparticles. Ultrasonic treatment provides a synthesis of non-porous materials and a homogeneous distribution of strengthening particles in the bulk material, thereby increasing the mechanical properties of pure aluminum. It is shown that the increase in the alloy hardness, yield stress, ultimate tensile strength, and lower plasticity depend on the average grain size and a greater amount of nanoparticles in the alloy.

Producing wear-resistant materials by SHS-casting with the application of centrifugal forces

The paper is devoted to the problem of producing hard, wear-resistant materials by SHS-casting using centrifugal forces. We have developed a device for centrifugal SHS casting and initial compositions of the reactive iron-base charge. A technology for producing coatings, materials and final products with a non-uniform distribution of strengthening particles over the specimen volume has been developed and tested in industrial conditions. The microstructure and phase composition of the synthesized material with a non-uniform distribution of reinforcing particles is studied. The synthesized material implements the Charpy principle: dispersed hard carbide particles are distributed in a relatively soft matrix, which ensures high wear resistance. By means of SHS casting, billets were obtained for producing a measurement instrument, namely a plug-type gauge, which successfully passed industrial tests at OJSC “VIZAS”. The tests shown that the hardness of all synthesized samples was in the range from 63 to 68 HRC and the number of measurements per 1 micron of wear on a diameter of15 mm was 2500 to 2700. Hence, the developed method made it possible to significantly increase the service life of the measuring tool: by a factor of 1.5 to 2.

TRIBOLOGICAL PROPERTIES AND MICROSTRUCTURE OF ELECTROLESS NICKEL COATINGS REINFORCED WITH NANOPARTICLES

Composite nickel coatings composed of Ni; Ni + TiN are studied. The method for elecrtroless nickel deposition EFFTOM-NICKEL with TiN nanosized strengthening particles (50nm) is applied. The coatings are deposited on austempered ductile iron (ADI) samples. The composition of cast iron samples is: Fe-3,63C-2,59Si-0,30Mn-0,010S-0,034P-0,53Cu wt. %. The samples are put under isothermal hardening at 900oС for an hour and isothermal retention at 290 oС for 2 hours with the aim to receive a lower bainite structure. The wear resistance experimental testing is carried out using Taber-Abraser test machine by disk to disk classical method. The microstructure observations of the coatings and padding are performed using an optical microscope GX41 OLIMPUS also the coatings’ microhardness by Knoop Method is examined. The wear resistance, microstructure, thickness and microhardness of the as plated and thermally processed at 290oС for 6 hours coatings are defined.

Numerical Modeling of the Hot Forming Process of Composite Materials

We present a fully coupled thermomechanical simulation of the hot forming process of composite materials. The raw material is a mixture of resin powders, strengthening particles and reinforcing fibers. Complex material responses in the process, such as phase change (melting and polymerization) and reorientation of the fibers, determine the microstructure and the performance of the final product. A phase-aware incremental mesh-free Lagrangian method is presented to overcome the challenges, which combines the Optimal Transportation Meshfree (OTM) method and the variational thermomechanical constitutive updates, and simulation results including the compression ratio, material properties of the final product and orientation distribution of fibers are recorded. By comparing the simulation results with the experimental measurements, the computational framework is validated, which enables robust and efficient analysis of the sensitivity of the performance of composite materials on their processing parameters.