Measurement of mechanical and fatigue properties using unified, simple-geometry specimens: Cold spray additively manufactured pure metals

A methodology that allows joint determination of fundamental engineering properties of materials/components vital to their efficient design and a safe service lifetime operation is presented. Using a combination of recently developed techniques, a simultaneous assessment of mechanical properties, fatigue crack growth rates, as well as fracture toughness is described. All these are performed using unified-geometry samples that are simple and easy to produce. The mechanical properties are measured in tensile and compressive modes, while the combination of developed bending test methods (quasi-static four-point bending and fatigue bending) enables to cover the fatigue loading from very low loads corresponding to crack propagation threshold values up to the high loads corresponding to a static fracture of the fracture toughness test. To validate and complement the bending data, additional resonant ultrasonic measurements of the corresponding properties are carried out. The methodology is partially suitable for testing of cold sprayed deposits. Therefore, Al, Cu, Ni and Ti deposits are tested and compared to cold-rolled sheet reference samples. The results are quantified in the form of NASGRO equation, widely used in software for prediction of fatigue lives. Together, the obtained set of data may be readily used for modeling of the performance of cold sprayed parts. Finally, fractographic analysis of the failed specimens is presented to describe the mechanisms leading to failure. At low loads, the reference sheets and the cold sprayed deposits exhibit similar behavior, where the cracks grow in a trans-crystalline mode without any significant interaction with deposit particle boundaries. Contrary to this, the behavior changes at higher loads: the particle interfaces in the cold sprayed deposits become the weak point and the cracks grow at high rates by inter-particle decohesion, while the sheet materials generally fail by striation mechanism at much lower rates

Increasing Fatigue Endurance of Hydroxyapatite and Rutile Plasma Sprayed Biocomponents by Controlling Deposition In-Flight Properties

Three sets of hydroxyapatite and rutile-TiO₂ coatings were plasma sprayed onto metallic substrates. The spray parameters of the sets were modified so as to obtain different in-flight temperatures and velocities of the powder particles within the plasma jet (ranging from 1778 to 2385 K and 128 to 199 ms⁻¹, respectively). Fatigue endurance of the coated specimens was then tested. The samples were subjected to a symmetric cyclical bend loading, and the crack propagation was monitored until it reached a predefined cross-section damage. The influence of the coating deposition was evaluated with respect to a noncoated reference set and the in-flight characteristics. Attributed to favorable residual stress development in the sprayed samples, it was found that the deposition of the coatings generally led to a prolongation of the fatigue lives. The highest lifetime increase (up to 46% as compared to the noncoated set) was recorded for the coatings deposited under high in-flight temperature and velocity. Importantly, this was achieved without significantly compromising the microstructure or phase composition of the deposited HA and TiO₂ layers.The experimental study was supported through Czech Science Foundation Grant GB14-36566G “Multidisciplinary research centre for advanced materials.” Financial support by the European Regional Development Fund in the frame of the project Centre of Advanced Applied Sciences (No. CZ.02.1.01/0.0/0.0/16_019/0000778) is gratefully acknowledged

Stříbrem dopovaný hydroxidapatitový povlak nanášený pomocí suspenzního plazmatického nástřiku

Čistá suspenze hydroxidapatatu byla vyrobena pomocí chemické sysntézy. S použitím WSP hořáku byl vytvořen HA povlak na substrátu z SS304 a Ti6Al4V. Vlastnosti povlaku byly hodnoceny pomocí SEM, XRD a EDX. PO dopozici bylo dosaženo 4-10% podílu amorfní fáze a 75-82% krystalické HA fáze v tloušťcě cca 145 um. Tribologické chování bylo hodnoceno pomocí testu pin-on-disc. Přídavek AgNO3 do suspenze vedl k vzniku Ag disperze mezi splaty v 8% podílu Ag. Úspěšné přidání antibakteriálního Ag je pokrokem v oblasti výzkumu materiálů kloubních náhrad.Pure hydroxyapatite suspension was produced by wet chemical synthesis. Using a hybrid water-stabilized torch, a series of HA coatings were produced on SS304 and Ti6Al4V substrates and their properties were characterized by SEM, EDX and XRD techniques. After deposition, the amorphous phase content reached 6-10% and the coatings retained 75-82% of crystalline HA phase. Their thickness reached 145 lm. To understand the wear behavior of the coatings, pin-on-disc tribology evaluation was performed. Additionally, a set of HA coatings was prepared with pure metallic Ag content. This formed by in situ chemical decomposition of AgNO3 added into the HA suspension. The Ag was dispersed evenly within the coatings in the form of submicron-sized particles situated predominantly along the HA splats boundaries with a total Ag content of 8 wt.%. Given the antibacterial properties of Ag, such result presents a promising step forward in the hard tissue replacement research