Microstructure and Mechanical Properties Change with Cold Rolling of New Ti-13Nb-1.5Ta-3Mo Alloy

In this paper, a new metastable Titanium alloy in the Ti-Nb-Ta-Mo system has been successfully produced using both the d-electron and Moeq concept. The influence of cold rolling on the microstructure and hardness was investigated. The alloy was fabricated by arc melting, cold rolled up to 90% reduction in thickness and characterized using X-ray diffraction (XRD), optical microscope and Vickers microhardness. The XRD peaks depicted both β and α′′ phases in all the cold rolled specimens. The hardness of the alloy increased with increasing cold rolling reduction thickness. An excellent plasticity (≥ 65%) and compressive strength up to (2.9 GPa) was achieved with low Young’s modulus (31 GPa) and no failure or crack on the alloy. Also, the alloy demonstrated a high compressive true strength coefficient (k ≈1426 MPa) along with improved strain hardening index (n ≈ 0.41). Based on the XRD, optical microscope and microhardness indentation micrographs, the deformation mechanism of Ti-13Nb-1.5Ta-3Mo was found to be a combination of stress induced transformation, mechanical twinning and slipping.

Crack-Resistance Behavior of an Encapsulated, Healing Agent Embedded Buffer Layer on Self-Healing Thermal Barrier Coatings

In this work, a novel thermal barrier coating (TBC) system is proposed that embeds silicon particles in coating as a crack-healing agent. The healing agent is encapsulated to avoid unintended reactions and premature oxidation. Thermal durability of the developed TBCs is evaluated through cyclic thermal fatigue and jet engine thermal shock tests. Moreover, artificial cracks are introduced into the buffer layer’s cross section using a microhardness indentation method. Then, the indented TBC specimens are subject to heat treatment to investigate their crack-resisting behavior in detail. The TBC specimens with the embedded healing agents exhibit a relatively better thermal fatigue resistance than the conventional TBCs. The encapsulated healing agent protects rapid large crack openings under thermal shock conditions. Different crack-resisting behaviors and mechanisms are proposed depending on the embedding healing agents.

Micromechanical Properties of UHMWPE’S with Different Molecular Weights

Ultrahigh molecular weight polyethylene (UHMWPE) is used as a key component of total joint replacements (TJR) and its mechanical performance is one of the factors influencing TJR lifetime. Micromechanical properties of three model UHMWPE samples with different molecular weights were evaluated from both non-instrumented and instrumented microindentation hardness testing. The properties were correlated with molecular and supermolecular structure of the samples. We have demonstrated that molecular weight influenced the final micromechanical properties mostly indirectly – it changed the overall crystallinity, which strongly correlated with microhardness, indentation modulus, and also with the elastic part of the indentation work. Only microcreep was influenced predominantly by amorphous phase, in which the higher molecular weight resulted in higher amount of entanglements and slightly higher creep resistance.

Friction Stir Welding of Aluminium Alloy Sheets

Aluminium alloy 7050 in a T7451 temper was friction-stir welded (FSW) to investigate the effects of different process parameters on the microstructure and mechanical properties. Butt joints were obtained in 10mm thick-sheets, keeping a constant rotational speed of 550 rpm. Weld power and torque were recorded for each weld in order to obtain the heat input of the process, since the final properties of the welds are strongly related to this variable. The joints were characterized by optical microscopy and microhardness indentation through the stir zone (SZ), thermo-mechanically affected zone (TMAZ), and heat affected zone (HAZ) at different cross section heights. The processing of FSW, the microstructure in FSW alloys and the factors influencing weld quality are introduced.

Experimental and Simulation Study of Microhardness Indentation of Solid Oxide Fuel Cell Using Progressive Damage Material Model

A finite element model with progressive damage material properties is proposed to study the mechanical behavior of Ni-8YSZ/8YSZ half-cell structures under Vickers indentation tests. The simulation results show that the simulated hardnesses of the as-received anode (NiO-8YSZ with 12% porosity) and the reduced anode (NiO-8YSZ with 36.68% porosity) samples were 2.54 GPa and 0.66 GPa, respectively, which are fairly in agreement with the experimental data. The interface delamination between the anode layer and the electrolyte layer was investigated by varying the mechanical properties of the interface between the two layers. The parametric study shows that a weak interfacial layer (with a low Young’s modulus) may cause potential failure due to delamination.

Development of Triphasic Calcium Phosphate–Carbon Nanotubes (HA/TCP-CNT) Composite: A Preliminary Study

Triphasic calcium phosphate, composed of a more stable phase hydroxyapatite (HA) and highly soluble tricalcium phosphates (α- and β-TCP) has been synthesized through hydrothermal method. In the present work, an in-situ method to disperse 1wt% multiwall carbon nanotubes (MWCNTs) within HA/TCP powder has been used in order to develop HA/TCP-CNTs composite. XRD results confirmed the formation of HA, α-TCP and β-TCP in both as-prepared powder and composite samples. The graphite peaks appeared in the composite samples as well. FTIR analysis of sintered compacted powder showed the formation of weak bands of PO43- as the temperature was increased. The sintered compacts were mechanically tested by Vickers microhardness indentation method. HA/TCP-CNTs composite was found to have a significant of Vickers Hardness of 1.98 GPa after 1100°C sintering. The morphology analysis showed that in-situ deposition technique provides homogeneous dispersion of CNTs in the calcium phosphate matrix.