Results for “tin” — Page 5

The effect of nitrogen content on the formation of an equiaxed solidification structure of Fe-16Cr steel was investigated. Moreover, two different kinds of refractory materials, i.e., alumina and magnesia, were employed to control the type of oxide inclusion. The characteristics of TiN(-oxide) inclusions were quantitatively analyzed in both molten steel and solidified samples. When the melting was carried out in the alumina refractory, the grain size continuously decreased with increasing nitrogen content. However, a minimum grain size was observed at a specific nitrogen content (approx. 150 ppm) when the steel was melted in the magnesia refractory. Most of the single TiN particles had a cuboidal shape and fine irregularly shaped particles were located along the grain boundary due to the microsegregation of Ti at the grain boundary during solidification. The type of TiN-oxide hybrid inclusion was strongly affected by the refractory material where Al{sub 2}O{sub 3}-TiN and MgAl{sub 2}O{sub 4}-TiN hybrid-type inclusions were obtained in the alumina and magnesia refractory experiments, respectively. The formation of oxide inclusions was well predicted by thermochemical computations and it was commonly found that oxide particles were initially formed, followed by the nucleation and growth of TiN. When the nitrogen content increased, the number density of TiN linearly increased in the alumina refractory experiments. However, the number of TiN exhibits a maximum at about [N] = 150 ppm, at which a minimum grain size was obtained in the magnesia refractory experiments. Therefore, the larger the number density of TiN, the smaller the primary grain size after solidification. The number density of TiN in the steel melted in the magnesia refractory was greater than that in the steel melted in the alumina refractory at given Ti and N contents, which was due to the lower planar lattice disregistry of MgAl{sub 2}O{sub 4}-TiN interface rather than that of Al{sub 2}O{sub 3}-TiN interface. When ∆T{sub TiN} (= difference between the TiN precipitation temperature and the liquidus of the steel) was 20 K to 40 K, the number density of effective TiN was maximized and thus, the grain size was minimized after solidification. Finally, although most of the TiN particles were smaller than 1 μm in the molten steel samples irrespective of the nitrogen content, TiN particles larger than 10 μm were observed in the solidified samples when the nitrogen content was greater than 150 ppm. The growth of TiN particles during melting and solidification was well predicted by the combinatorial simulation of the ‘Ostwald ripening model’ based on the Lifshitz–Slyozov–Wagner theory in conjunction with the ‘Diffusion controlled model’ using Ohnaka’s microsegregation equation.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Precipitation Behaviors of TiN Inclusion in GCr15 Bearing Steel Billet

There are many types of non-metallic TiN-based inclusions observed in GCr15 bearing steel, including single-particle TiN, multi-particle polymerized TiN, and complex inclusions like TiN-MnS, TiN-MgO-MgAl{sub 2}O{sub 4} (TiN-MgO-MA), and TiN-MgAl{sub 2}O{sub 4}-MnS (TiN-MA-MnS). Thermodynamic calculations suggest that single-particle TiN precipitates dominate the mushy zone of GCr15 bearing steel. Kinetic calculations regarding TiN growth suggest that the final size of the single-particle TiN ranges between 1 and 6 μm in the initial concentration range of [pct Ti] = 0.0060 to 0.0079 and [pct N] = 0.0049 to 0.0070, at 1620 to 1640 K and a local cooling rate of 0.5 to 10 K/s. The multi-particle polymerized TiN are formed by single TiN particles in three stages: single-particle TiN inclusions approach each other drawn by the cavity bridge force (CBF), local active angles consolidate, and neck region sintering occurs. Based on the thermodynamic calculations of TiN, MnS, and MgO precipitation, the formation behaviors of complex inclusions of TiN-MnS, TiN-MgO-MA, and TiN-MA-MnS were investigated.

36 MATERIALS SCIENCE↗

DOE OSTI2019

Cathodic Cage Plasma Pre-treatment of TiN-Coated AISI-304 Stainless Steel for Enhancement of Mechanical Strength and Wear Resistance

Although austenitic stainless steels (ASSs) are known for their superior corrosion resistance properties, the use of such materials in motion contact parts is limited due to their low wear resistance. Previous studies reveal that titanium nitride (TiN) coating of ASS significantly improves its hardness and surface morphology but not the wear resistance due to weak interfacing with the substrate. Since plasma nitriding is a flexible and multifunctional case-hardening process, an attempt was made to improve the wear resistance of TiN-coated AISI-304 stainless steel by subjecting it to pre-treatment by pulsed DC cathodic cage plasma nitriding (CCPN) in the abnormal glow region. The hardness of the TiN-coated steel samples (with and without CCPN pre-treatment) was measured using Vickers micro-hardness tester. This test revealed maximum hardness of 2284 HV after plasma treatment of TiN-coated steel. The untreated TiN-coated steel exhibited 10.6 times lower hardness than the plasma pre-treated TiN-coated steel (CCPN-TiN). XRD analysis of the untreated TiN-coated steel showed strong diffraction peaks of TiN (311) and (400) in the spectrum, whereas plasma pre-treated sample contained dominant peaks of TiN (111), (200) and (220). The ball-on-disk wear tester was used to investigate the wear behavior of the samples. Very small wear rate and friction coefficient were reported for CCPN-TiN-coated steel. The observed low wear rate was probably due to the development of a subsurface (i.e., nitrided surface) on TiN-coated steel during CCPN pre-treatment.

36 MATERIALS SCIENCE↗

DOE OSTI2018

In Situ Observation of the Precipitation, Aggregation, and Dissolution Behaviors of TiN Inclusion on the Surface of Liquid GCr15 Bearing Steel

In this study, the precipitation, aggregation, and dissolution behaviors of TiN inclusions on the surface of liquid GCr15 bearing steel have been investigated by combining the observations of confocal laser scanning microscope (CLSM) and field emission scanning electron microscope (FE-SEM) with those obtained from energy dispersive spectrometer (EDS) and theoretical analysis. The kinetic results show that the initial concentration of Ti and N are 0.0078 and 0.0049, respectively, the precipitation temperature is between 1640 K and 1680 K (1367 °C and 1407 °C), and the local cooling rate is between 0.5 and 10 K/s; TiN inclusion can precipitate only when the solid fraction is higher than 0.847 and its precipitation radius is between 1 and 6 μm. The precipitation radius of a TiN inclusion in the GCr15 bearing steel sheet can be reduced by decreasing the N content and increasing the cooling strength. The aggregation and densification of multi-particle aggregated TiN inclusions are verified by CLSM observation and theoretical analysis. The inclusions are aggregated by the cavity bridge force (CBF), and the aggregated TiN is formed by solid-phase sintering. The results of force analysis show that CBF plays a dominant role in the aggregation process of the inclusions. The atomic ratio of Ti and V obtained by EDS is 18:1, which may melt TiN and form the liquid inclusion at 1688 K (1415 °C) observed by CLSM. The theoretical analysis is conducted for the dissolution of the TiN inclusions observed by CLSM, which shows that the dissolution of the TiN inclusions is related to the size of the inclusions; the larger the size, the greater the dissolution rate. The long-strip TiN inclusion may be formed by the Ostwald ripening of two TiN inclusions. The TiN inclusions smaller than 3 μm in the GCr15 bearing steel may be formed by the dissolved Ti and N generated by the dissolution of TiN.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Long-term thermal aging of parylene conformal coating under high humidity and its effects on tin whisker mitigation

Usage of pure tin (Sn) or Sn-rich alloy in electronics industry is growing, which makes them more susceptible to the spontaneous growth of tin whiskers. The risk of having these whiskers can be dramatically mitigated by applying a conformal coating provided that it not only possesses excellent mechanical and adhesion properties but also maintains these properties throughout their service. Parylene C is commonly used as a conformal coating because of its favorable mechanical and physical properties, as well as superior conformal coverage. The purpose of this paper is to investigate the degradation of parylene C coating during the thermal aging in high humidity environment (85°C/85% relative humidity for up to 5000hrs) and its effect on the tin whisker mitigation capacity. It was observed that during aging at high temperature and high humidity (HTHH) environment, the oxidation occurs at early times, followed by bond scission, resulting in the loss of strength of the coating. Thinner parylene coating (12.5-μm-thick) had better coating adhesion on the silane-treated tin surface, so provided the better protection for tin whisker penetration than the thicker counterpart (25-μm-thick). After 2500hrs of aging, due to the degradation of the silane agent at the tin/parylene interface, the adhesion of the parylene coating was significantly weakened on the tin surface, which resulted in extensive corrosion of the tin solderpads. The loss of adhesion of the coating, along with the corrosion of the tin surface facilitated the tin whisker nucleation at the interface while the loss of mechanical strength and the brittleness made the coating easily penetrated by the growing whiskers. Tin whiskers with a smaller diameter were buckled and grew along the delaminated region while those with a larger diameter penetrated and continued to grow through the coating. Hence, the effectiveness of the parylene coatings on tin whisker mitigation is significantly reduced under long exposure to such high temperature and high humidity.

36 MATERIALS SCIENCE↗

DOE OSTI2014

Effect of pulse frequency on microstructural, nanomechanical, and wear properties of electrodeposited Ni–TiN composite coatings

The current paper reports successful syntheses of Ni–TiN composite coatings by pulse electrodeposition. The effect of pulse frequency on the microstructures, nanomechanical, and wear properties of the coatings was investigated using transmission electron microscopy, X–ray diffraction, nanoindenter, scanning electron microscopy, and wear test instrument. The results showed that the Ni–TiN composite coating prepared at the pulse frequency of 100 Hz showed the presence of a less number of TiN particles and some degrees of aggregation in micro-regions. By contrast, in the Ni–TiN coating deposited at the pulse frequency of 500 Hz, the TiN particles were large in number and dispersed homogeneously, thereby, offering the coating a uniform and fine structure. The average grain diameters of Ni and TiN in the coating prepared at 100 Hz were 154.7 and 44.8 nm, respectively, whereas those for the coating prepared at 500 Hz were 67.3 and 25.9 nm, respectively. The maximum TiN content in the Ni-TiN coating deposited at 800 Hz was approximately 10.5 wt. %. The maximum microhardness and the Young's modulus values for the Ni–TiN composite coatings deposited at 800 Hz were 35.7 GPa and 167.4 GPa, respectively. Furthermore, the Ni–TiN composite coating prepared at 100 Hz had more severe damages, whereas the morphologies of worn surface of the coatings deposited at 500 Hz and 800 Hz were smooth and only a few small pits appeared on the surface.

36 MATERIALS SCIENCE↗

NASA NTRS2000

Effects of Conformal Coat on Tin Whisker Growth

A whisker from a tin plated part was blamed for the loss of a commercial spacecraft in 1998. Although pure tin finishes are prohibited by NASA, tin plated parts, such as hybrids, relays and commercial off the shelf (COTS) parts, are something discovered to have been installed in NASA spacecraft. Invariably, the assumption is that a conformal coat will prevent the growth of, or short circuits caused by, tin whiskers. This study measures the effect a Uralane coating has on the initiation and growth of tin whiskers, on the ability of this coating to prevent a tin whisker from emerging from the coating, and on the ability to prevent shorting. A sample of fourteen brass substrates (1 inch by 4 inches by 1/16 inch) were plated by two separate processes: half of the specimens were 'bright' tin plated directly over the brass substrate and half received a copper flash over the brass substrate prior to 'bright' tin plating. Each specimen was coated on one half of the substrate with three bi-directional sprays of Uralane 5750 to a nominal thickness of 25 to 75 micrometers (1 to 3 mils). Several specimens of both types, Cu and non-Cu flashed, were placed in an oven maintained at 50 C as others' work suggests that this is the optimal temperature for whisker formation. The remaining specimens were maintained at room ambient conditions. The surfaces of each specimen have been regularly inspected using both optical (15 to 400x power) and Scanning Electronic Microscopy (SEM). Many types of growths, including needle-like whiskers, first appeared approximately three months after plating on the non-conformally coated sides of all specimens. At four months, 4 to 5 times more growth sites were observed on the coated side; however, the density of growth sites on the non-conformally coated side has since increased rapidly, and now, at one year, is about the same for both sides. The density of growth sites is estimated at 90/sq mm with 30 percent of the sites growing whiskers (needle-like forms) with the potential to cause short circuit bridging. The average growth rate of the needle-like whiskers on the non-conformally coated areas is about 130 micrometers per year with some outliers reaching 800 micrometers after one year. It is more difficult to make growth measurements under the conformal coat. As yet no whiskers have been observed to penetrate through the coating surface, however, a number of tin nodules appear on the verge of breaking through the thinner regions of the coating surface. These domes are developing sharper and sharper tips, as if a growing whisker is about to push its way through a tough skin. Our observations are that the specimens with copper flash show a much lower density of nucleation sites and significantly slower whisker growth compared to the specimens that have only bright tin plating over brass. The specimens kept at room temperature have a higher whisker density than those stored at 50 C. This is an unexpected result and does not agree with the published findings of others. All of the whiskers originate from small surface defects (thin, tiny scratches) that appear over the entire surface of each specimen.

Kadesch, Jong S.↗

NASA NTRS2010

Estimating the Probability of Electrical Short Circuits from Tin Whiskers

To comply with lead-free legislation, many manufacturers have converted from tin-lead to pure tin finishes of electronic components. However, pure tin finishes have a greater propensity to grow tin whiskers than tin-lead finishes. Since tin whiskers present an electrical short circuit hazard in electronic components, simulations have been developed to quantify the risk of said short circuits occurring. Existing risk simulations make the assumption that when a free tin whisker has bridged two adjacent exposed electrical conductors, the result is an electrical short circuit. This conservative assumption is made because shorting is a random event that had an unknown probability associated with it. Note however that due to contact resistance electrical shorts may not occur at lower voltage levels. In our first article we developed an empirical probability model for tin whisker shorting. In this paper, we develop a more comprehensive empirical model using a refined experiment with a larger sample size, in which we studied the effect of varying voltage on the breakdown of the contact resistance which leads to a short circuit. From the resulting data we estimated the probability distribution of an electrical short, as a function of voltage. In addition, the unexpected polycrystalline structure seen in the focused ion beam (FIB) cross section in the first experiment was confirmed in this experiment using transmission electron microscopy (TEM). The FIB was also used to cross section two card guides to facilitate the measurement of the grain size of each card guide's tin plating to determine its finish .

Courey, Karim J.↗

NASA NTRS2009

Developing an Empirical Model for Estimating the Probability of Electrical Short Circuits from Tin Whiskers

To comply with lead-free legislation, many manufacturers have converted from tin-lead to pure tin finishes of electronic components. However, pure tin finishes have a greater propensity to grow tin whiskers than tin-lead finishes. Since tin whiskers present an electrical short circuit hazard in electronic components, simulations have been developed to quantify the risk of said short circuits occurring. Existing risk simulations make the assumption that when a free tin whisker has bridged two adjacent exposed electrical conductors, the result is an electrical short circuit. This conservative assumption is made because shorting is a random event that had an unknown probability associated with it. Note however that due to contact resistance electrical shorts may not occur at lower voltage levels. In our first article we developed an empirical probability model for tin whisker shorting. In this paper, we develop a more comprehensive empirical model using a refined experiment with a larger sample size, in which we studied the effect of varying voltage on the breakdown of the contact resistance which leads to a short circuit. From the resulting data we estimated the probability distribution of an electrical short, as a function of voltage. In addition, the unexpected polycrystalline structure seen in the focused ion beam (FIB) cross section in the first experiment was confirmed in this experiment using transmission electron microscopy (TEM). The FIB was also used to cross section two card guides to facilitate the measurement of the grain size of each card guide's tin plating to determine its finish.

Courey, Karim J.↗

DOE OSTI2019

Redox and structural controls on tin isotopic fractionations among magmas

Recent analytical developments have made possible the determination of the isotopic composition of tin in igneous rocks. In order to establish a framework to interpret the mass-dependent tin isotopic signatures of planetary materials, in this work, seven geologically-relevant silicate glasses (basalt, rhyolite, enstatite and anorthite glasses) were synthesized with moderate amounts of 119 Sn (on the order of a weight percent). Redox conditions were controlled during sample synthesis to set the redox ratio (Sn 2+ /Sn tot ) from stannous (Sn 2+ ) to stannic (Sn 4+ ) glasses. The mean force constants of tin bonds in these glasses were determined by synchrotron nuclear resonant inelastic X-ray scattering (NRIXS) in order to determine the reduced isotopic partition function ratios (β-factors) of these glasses. Clues on the coordination chemistry and the valence state of tin in these glasses were also derived from synchrotron Mossbauer spectroscopy (SMS). The force constants of tin drastically increases from Sn 2+ -bearing to Sn 4+ -bearing glasses and varies significantly with the glass composition at a given redox state. The average coordination number of tin likely controls these variations with glass composition as suggested by SMS results. It is concluded that large isotope fractionation is expected between materials containing Sn 2+ and Sn 4+ respectively even at magmatic temperatures and that the coordination chemistry of tin in silicates strongly affect its isotope partitioning behavior. Our experimental data are finally used to interpret available Sn isotope data collected in terrestrial rocks. The incompatible behavior of Sn 4+ in mantle minerals leads to a enrichment in heavy isotopes in mantle melts and to the depletion in heavy isotopes in solid residues of melting with a magnitude consistent with the isotope fractionation between Sn 2+ and Sn 4+ predicted by NRIXS data. Finally, we show that during fractional crystallization of basalt and considering the effect of tin coordination number in minerals and melts, the partitioning of Sn 4+ into ilmenite leads to an enrichment in light isotopes in the residual melt.

58 GEOSCIENCES↗

NASA NTRS2009

Estimating the Probability of Electrical Short Circuits from Tin Whiskers

To comply with lead-free legislation, many manufacturers have converted from tin-lead to pure tin finishes of electronic components. However, pure tin finishes have a greater propensity to grow tin whiskers than tin-lead finishes. Since tin whiskers present an electrical short circuit hazard in electronic components, simulations have been developed to quantify the risk of said short circuits occurring. Existing risk simulations make the assumption that when a free tin whisker has bridged two adjacent exposed electrical conductors, the result is an electrical short circuit. This conservative assumption is made because shorting is a random event that had an unknown probability associated with it. Note however that due to contact resistance electrical shorts may not occur at lower voltage levels. In our first article we developed an empirical probability model for tin whisker shorting. In this paper, we develop a more comprehensive empirical model using a refined experiment with a larger sample size, in which we studied the effect of varying voltage on the breakdown of the contact resistance which leads to a short circuit. From the resulting data we estimated the probability distribution of an electrical short, as a function of voltage.

Courey, Karim J.↗

DOE OSTI2019

Atomic Layer-Deposited Al{sub 2}O{sub 3} Interlayer for Improved Tribological and Anti-corrosion Properties of TiN Hard Coating on 316L Stainless Steel

A dense Al{sub 2}O{sub 3} interlayer was inserted into TiN to enhance the tribological and anti-corrosion properties of TiN hard coating via a hybrid process of magnetron sputtering and atomic layer deposition (ALD). The influence of the ALD-Al{sub 2}O{sub 3} layer on the microstructure, mechanical, tribological and anti-corrosion properties of TiN was examined. The TiN-Al{sub 2}O{sub 3} coating exhibits low friction coefficient and specific wear rate, due to the structure change and columnar refinement caused by the addition of amorphous ALD-Al{sub 2}O{sub 3} interlay which improves the mechanical properties of hard coating. The improved corrosion properties of TiN are attributed to the fact that the insulating ALD-Al{sub 2}O{sub 3} used as a sealing layer can prevent the corrosive chlorine ions migrating into the lower TiN layer and block the charge transport in coatings. Moreover, raising the insertion position of ALD-Al{sub 2}O{sub 3} layer away from the steel substrate results in a further increase in the anti-corrosion property of TiN-Al{sub 2}O{sub 3} composite coating.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Stability of Tin-Lead Halide Perovskite Solar Cells

Tin-lead perovskites have low band gaps (1.2 eV - 1.4 eV) that offer complementary absorption spectra to mixed halide perovskites with band gaps in the range of 1.6 eV - 1.85 eV. In combination, tin-lead and mixed halide perovskites can be used to make efficient all-perovskite tandem solar cells. While these can achieve high efficiency, they are hampered by the unproven longterm stability of tin-containing perovskites. We make the first demonstration of tin-lead perovskite solar cells that pass benchmark 1000-hour tests of stability under stressors of heat, light, and atmospheric exposure. We identify that mixed tin-lead perovskites oxidise by a different chemical pathway, one that is much less favourable, than the oxidation pathway followed by pure tin perovskites, making them significantly more stable. Fortuitously, mixed tin-lead perovskites also have band gaps that are close to ideal for the rear cell of an all-perovskite monolithic two-junction tandem. Beyond selecting the composition of the perovskite to be one that has inherently suppressed tendency to oxidise, we also fabricate a novel heterojunction-based architecture that eliminates the commonly used acidic PEDOT:PSS layer, which leads to enhanced stability. By packaging the resulting solar cell in a glass-on-glass package with a pliable low-elastic-modulus polyolefin encapsulant and a butyl rubber edge seal, we also demonstrate that the low band gap perovskite solar cell that passes the IEC damp heat test for thin film solar cells - a milestone that demonstrates the removal of a significant impediment to the commercialization of high efficiency perovskite tandem solar cells.

14 SOLAR ENERGY↗