Addition of Sn to TiNb alloys to improve mechanical performance and surface properties conducive to enhanced cell activity

Titanium (Ti) alloys with Niobium (Nb) and Tin (Sn) were prepared in order to conduct a systematic study on the bulk and surface properties of as-cast c.p.Ti, binary Ti40Nb and Ti10Sn, and ternary Ti-10Nb-5Sn (at.%) to ascertain whether Sn content can be used as an enhancer for cell activity. From a metallurgy viewpoint, a range of binary and ternary alloys displaying distinctive Ti phases (i.e. β, α’, α”) were achieved at room temperature. Their surface (oxide thickness and composition, roughness, contact angle) and bulk (compressive stiffness, strength, elongation, microhardness, electrical resistance) features were characterised. The same surface roughness was imparted on all the alloys, therefore substrate-cell interactions were evaluated independently from this variable. The physico-mechanical properties of the ternary alloy presented the highest strength to stiffness ratio and thereby proved the most suitable for load-bearing orthopaedic applications. From a cellular response viewpoint, their cytotoxicity, ability to adsorb proteins, to support cell growth and to promote proliferation were studied. Metabolic activity using a mouse model was monitored for a period of 12 days to elucidate the mechanism behind an enhanced proliferation rate observed in the Sn-containing alloys. It was hypothesised that the complex passivating surface oxide layer and the bulk inhomogeneity with two dominant Ti phases were responsible for this phenomenon

Diffusion barrier characteristics of Ni-NbOx composite electrodeposits for liquid In-Sn solder interconnects

The control of interfacial microstructural stability is of utmost importance to the reliability of liquid solder interconnects in high temperature electronic assemblies. This is primarily due to excessive intermetallic compounds (IMCs) that can form and continuously grow during high temperature operation, which renders conventional barrier metallizations inadequate. With the intention of reducing such excessive IMC growth, electrically conducting, NbOx containing Ni coatings were developed using electrodeposition and were assessed as solder diffusion barrier layers in terms of their electrical conductivity and barrier property. The present work adopts a novel electrochemical route to produce Ni-NbOx composite coatings of good uniformity, compactness and purity, from non-aqueous glycol-based electrolytes consisting of NiCl2 and NbCl5 as metal precursors. The effects of cathodic current density and NaBH4 concentrations on the surface morphology, composition and thickness of the coatings were examined. Increased NaBH4 concentrations were found to elevate the maximum deposit thickness (above 10 μm), although these led to a reduction in the co-deposited Nb content. The composite coatings generally exhibited good electrical conductivity. The reaction between a liquid 52In-48Sn solder and Ni-NbOx, with Nb contents up to 6 at.%, was studied at 200°C. The results indicate that, Ni-NbOx with sufficient layer thickness and higher Nb content, offered longer service lifetime. Nb enrichment was generally observed at or close to the reaction front after high temperature storage which suggests evident effectiveness of the enhanced diffusion barrier characteristics. A mechanism for the role of Nb as a barrier performance enhancer was postulated

Interfacial reaction and microstructural evolution between Au-Ge solder and electroless Ni-W-P metallization in high temperature electronics interconnects

© 2017 IEEE. The elevated working temperature of high temperature electronics can inevitably cause potential excessive growth of interfacial intermetallic compounds (IMCs), which can significantly deteriorate the mechanical integrity of electronic devices. Therefore, a robust diffusion barrier that can operate reliably under elevated temperature is highly demanded to retard the interfacial reaction between solder and substrate. In this work, a ternary Ni-W-P alloy was deposited through electroless plating and applied as an Under Bump Metalisation (UBM) to Au-Ge solder joints. The interfacial reaction in Au-Ge/Ni-W-P solder joints after reflow and prolonged ageing durations was investigated. We found NiGe and Ni5Ge3 layers formed after reflow, however only NiGe was observed after 1000h aging at 300°C. The thickness of NiGe increases linearly with the square root of ageing time up to 1500h, indicating that the growth mechanism of NiGe is diffusion-control process when Ge atoms are sufficient. After ageing for 2000h, although Ge atoms from Au-Ge solder was fully consumed, the Ni-W-P coating remained stable and exhibited excellent diffusion barrier property. During various ageing durations, the top-view morphology of NiGe IMC grains changed from pyramid-like and polygon-like shape at as-built stage to granulate-like (up to 1500h), and finally a polygon-like shape (after 2000h)

Combined effects of surface oxidation and interfacial intermetallic compound growth on solderability degradation of electrodeposited tin thin films on copper substrate due to isothermal ageing

© 2018 Elsevier Ltd We report new insights into the solder wettability degradation of Sn thin films on Cu under 155 °C isothermal ageing. A multiscale wettability degradation model was established, reflecting quantitatively the surface oxidation and interfacial intermetallic compound (IMC) growth, on the basis of solder wetting behaviour. The thermal oxidation of Sn exhibited heterogeneous inward thickening, lateral expanding and outward platelet-like growth, forming nanocrystalline, oxygen-deficient SnO2with pronounced voiding/cracking propensity. Unlike a commonly held belief that the initial wettability loss is due to surface-exposing and oxidation of IMCs, it was found from dual combined effects of inward surface oxidation and outward IMC growth

An investigation into the effect of dry bake on the solderability degradation of electrodeposited tin finishes

The solderability of component termination finishes degrades upon storage due to the combined effects of surface contamination, oxidation, corrosion and/or intermetallic compound (IMC) formation at the interface between substrate and finishes. Such solderability degradation impinges on the shelf-life of the electronics components and hence demands an in-depth understanding to ensure high reliability Pb-free soldering. This paper is concerned with the effect of the 155°C dry bake precondition on the accelerated ageing of bright Sn electrodeposited termination finishes over Cu substrates. Two coating thicknesses, 2.5 μm and 9 μm, were studied as-received and dry baked for 4 hr and 16 hr as per industrial standards and analysed with respect to their solderability, microstructural and compositional characteristics. It was found that, with increasing dry bake time, both the thickness variations experienced continued solderability degradation, with only the 2.5 μm thick coatings failed after 16 hr of dry heat. Such a loss of solderability was primarily contributed to the exposing of Sn-Cu IMCs. The thickness safety margin (i.e. maximum IMC thickness) for the dry bake condition (16 hr) of the given bright Sn samples was identified to be around 2.5 μm, which could provide a guidance for any future industrial initiative to further reduce coating thickness. Besides, the dry bake conditions have proven to be a consistent and reliable precondition approach for the Sn-based metal finishe

Atomic layer deposition (ALD) for tin whisker mitigation on Pb-free surfaces

Atomic layer deposition (ALD) for tin whisker mitigation on Pb-free surface

In-silico design and experimental validation of TiNbTaZrMoSn to assess accuracy of mechanical and biocompatibility predictive models

Numerical design of TiNbTaZrMoSn alloy preceded its manufacture and mechanical, physico-chemical and in vitro characterisation. The specifications of the alloy required a multi-objective optimisation including lower modulus of elasticity than c.p.Ti, high strength, stabilised crystal structure with a low martensitic start temperature, a narrow solidification range and high biocompatibility. The results reveal that there was a good match between the bulk mechanical properties exhibited by the alloy experimentally and those predicted. Regarding surface properties, independent of roughness effects, the oxide thickness and surface zeta-potential, measured in biologically relevant electrolytes and at physiological pH, appear as important factors in osteoblastic activity (i.e., cell proliferation, measured via DNA, protein and metabolite content, and differentiation, via ALP levels), but not in cell adhesion and viability. The thinner oxide layer and lower absolute value of surface zeta-potential on the TiNbTaZrMoSn alloy explain its lesser osteogenic properties (i.e., inhibition of ALP activity) compared to the c.p. Ti. This study demonstrates that the numerical models to predict microstructure and bulk mechanical properties of -Ti alloys are robust, but that the prediction of cellular bioactivity lags behind and still requires parameterisation to account for features such as oxide layer composition and thickness, electro-chemical properties and surface charge, and topography to optimise cell response in silico before committing to the costly manufacture and deployment of these alloys in regenerative medicine

Template-free, microscale dimple patterning of pure titanium surface through anodic dissolution using non-aqueous ethylene glycol-TiCl₄ electrolytes

We report a single-step anodic dissolution route for the template-free patterning of pure titanium (Ti) surfaces into a microscale, dimpled topography using non-aqueous ethylene glycol-TiCl4 electrolytes. Anodic dissolution of Ti metal (i.e. 0.04 M Ti4+) into a 40 EG: 1 TiCl4 electrolyte was found to induce a predominant change in the anodic dissolution reaction of Ti metal, converting its surface morphology from a slightly-pitted, bright finish into a dimple-patterned surface. The dimple pattern, ca. 4.5 µm in size and 1 µm in cusp height, was found self-organised with no apparent relation to underlying metal grain structure and independent of the applied potential within the anodic current plateau. The origin of the dimple patterning is surmised to arise from a dynamic self-organisation of the double layer, templated via tracery anodic reaction products – Ti-glycolate-derived, stacked-nanolayers (SNLs)

Supplementary Information files for: In-silico design and experimental validation of TiNbTaZrMoSn to assess accuracy of mechanical and biocompatibility predictive models

Supplementary Information files for: In-silico design and experimental validation of TiNbTaZrMoSn to assess accuracy of mechanical and biocompatibility predictive modelsNumerical design of TiNbTaZrMoSn alloy preceded its manufacture and mechanical, physico-chemical and in vitro characterisation. The specifications of the alloy required a multi-objective optimisation including lower modulus of elasticity than c.p.Ti, high strength, stabilised crystal structure with a low martensitic start temperature, a narrow solidification range and high biocompatibility. The results reveal that there was a good match between the bulk mechanical properties exhibited by the alloy experimentally and those predicted. Regarding surface properties, independent of roughness effects, the oxide thickness and surface zeta-potential, measured in biologically relevant electrolytes and at physiological pH, appear as important factors in osteoblastic activity (i.e., cell proliferation, measured via DNA, protein and metabolite content, and differentiation, via ALP levels), but not in cell adhesion and viability. The thinner oxide layer and lower absolute value of surface zeta-potentialon the TiNbTaZrMoSn alloy explain its lesser osteogenic properties (i.e., inhibition of ALP activity) compared to the c.p. Ti. This study demonstrates that the numerical models to predict microstructure and bulk mechanical properties of -Ti alloys are robust, but that the prediction of cellular bioactivity lags behind and still requires parameterisation to account for features such as oxide layer composition and thickness, electro-chemical properties and surface charge, and topography to optimise cell response in silico before committing to the costly manufacture and deployment of these alloys in regenerative medicine.<br

Use of mechanical alloying to develop novel titanium alloy powders suitable for the selective laser melting process

Over recent years there has been a push to develop Titanium (Ti) implants with a customised compressive modulus that would mimic that of load bearing bones (i.e. 10-30 GPa). One of the approaches suggested to achieve the desired properties is by alloying Ti with biocompatible alloying elements, such as Niobium (Nb), at bespoke quantities. These alloys can then be used in Selective Laser Melting (SLM) and other AM processes, provided they have suitable particle size distributions, chemical homogeneity, and flowability. Commercial powders for AM are typically produced by atomisation routes, but this process is not financially viable unless large quantities of powdered material are produced, and therefore not suitable for small scale production such as a one-off patientspecific implant. This study assesses the feasibility of using low-volume, mechanically alloyed powders, of target Ti-Nb compositions for use in a SLM process.It investigates the particle distribution and flowability of the produced powders as well as the densification and microstructural properties of parts fabricated with them, using an array of physical and chemical tools and techniques