Deposition and characterization of CrN/Si3N4 and CrAlN/Si3N4 nanocomposite coatings prepared using reactive DC unbalanced magnetron sputtering

Nanocomposite coatings of CrN/Si₃N₄ and CrAlN/Si₃N₄ with varying silicon contents were synthesized using a reactive direct current (DC) unbalanced magnetron sputtering system. The Cr and CrAl targets were sputtered using a DC power supply and the Si target was sputtered using an asymmetric bipolar-pulsed DC power supply, in Ar + N₂ plasma. The coatings were approximately 1.5 μm thick and were characterized using X-ray diffraction (XRD), nanoindentation, X-ray photoelectron spectroscopy and atomic force microscopy. Both the CrN/Si₃N₄ and CrAlN/Si₃N₄ nanocomposite coatings exhibited cubic B1 NaCl structure in the XRD data, at low silicon contents (< 9 at.%). A maximum hardness and elastic modulus of 29 and 305 GPa, respectively were obtained from the nanoindentation data for CrN/Si₃N₄ nanocomposite coatings, at a silicon content of 7.5 at.%. (cf., 24 and 285 GPa, respectively for CrN). The hardness and elastic modulus decreased significantly with further increase in silicon content. CrAlN/Si₃N₄ nanocomposite coatings exhibited a hardness and elastic modulus of 32 and 305 GPa, respectively at a silicon content of 7.5 at.% (cf., 31 and 298 GPa, respectively for CrAlN). The thermal stability of the coatings was studied by heating the coatings in air for 30 min in the temperature range of 400-900 °C. The microstructural changes as a result of heating were studied using micro-Raman spectroscopy. The Raman data of the heat-treated coatings in air indicated that CrN/Si₃N₄ and CrAlN/Si₃N₄ nanocomposite coatings, with a silicon content of approximately 7.5 at.% were thermally stable up to 700 and 900 °C, respectively.     

Electroless ternary Ni-W-P alloys containing micron size Al2O3 particles

In the present investigation electroless ternary NiWP-Al₂O₃ composite coatings were prepared using an electroless nickel bath. Second phase alumina particles (1 µm) were used to codeposit in the NiWP matrix. Nanocrystalline ternary NiWP alloys and composite coatings were obtained using an alkaline citrate based bath which was operated at pH 9 and temperature at 88 ± 2 °C. Mild steel was used as a substrate material and deposition was carried out for about 4 h to get a coating thickness of 25 ± 3 µm. Metallographic cross-sections were prepared to find out the coating thickness and also the uniform distribution of the aluminum oxide particles in NiWP matrix. Surface analysis carried out on both the coatings using scanning electron microscope (SEM) showed that particle incorporation in ternary NiWP matrix has increased the nodularity of composite coatings compared to fine nodular NiWP deposits. Elemental analysis of energy dispersive X-ray (EDX) results showed that codeposited P and W elements in plain NiWP deposit were 13 and 1.2 wt.%, respectively. There was a decrease in P content from 13 to 10 wt.% with a marginal variation in the incorporated W (1.01 wt.%) due to the codeposition of aluminum oxide particles in NiWP matrix. X-ray diffraction (XRD) studies carried out on as-plated deposits showed that both the deposits are X-ray amorphous with a grain size of around 3 nm. Phase transformation studies carried out on both the coatings showed that composite coatings exhibited better thermal stability compared to plain NiWP deposits. From the XRD studies it was found that metastable phases such as NiP and Ni₅P₂ present in the composite coatings heat treated at major exothermic peak temperature. Annealed composite coatings at various temperatures revealed higher microhardness values compared to plain NiWP deposits.     

Effects of K2O-Li2O doping on surface and catalytic properties of Fe2O3/Cr2O3 system

The effects of K₂O and Li₂O-doping (0.5, 0.75 and 1.5 mol%) of Fe₂O₃/Cr₂O₃ system on its surface and the catalytic properties were investigated. Pure and differently doped solids were calcined in air at 400-600 °C. The formula of the un-doped calcined solid was 0.85Fe₂O₃:0.15Cr₂O₃. The techniques employed were TGA, DTA, XRD, N₂ adsorption at −196 °C and catalytic oxidation of CO oxidation by O₂ at 200-300 °C. The results revealed that DTA curves of pure mixed solids consisted of one endothermic peak and two exothermic peaks. Pure and doped mixed solids calcined at 400 °C are amorphous in nature and turned to α-Fe₂O₃ upon heating at 500 and 600 °C. K₂O and Li₂O doping conducted at 500 or 600 °C modified the degree of crystallinity and crystallite size of all phases present which consisted of a mixture of nanocrystalline α- and γ-Fe₂O₃ together with K₂FeO₄ and LiFe₅O₈ phases. However, the heavily Li₂O-doped sample consisted only of LiFe₅O₈ phase. The specific surface area of the system investigated decreased to an extent proportional to the amount of K₂O and Li₂O added. On the other hand, the catalytic activity was found to increase by increasing the amount of K₂O and Li₂O added. The maximum increase in the catalytic activity, expressed as the reaction rate constant (k) measured at 200 °C, attained 30.8% and 26.5% for K₂O and Li₂O doping, respectively. The doping process did not modify the activation energy of the catalyzed reaction but rather increased the concentration of the active sites without changing their energetic nature.     

Influence of normal load and sliding speed on the tribological property of amorphous carbon nitride coatings sliding against Si3N4 balls in water

Amorphous carbon nitride (a-CN_x) coatings were deposited on Si₃N₄ disks by an ion beam assisted deposition system. The composition, structure and hardness of the a-CN_x coatings were characterized by Auger electronic spectroscopy, Raman spectroscopy and nano-indentation tester, respectively. The influences of normal load and sliding speed on the friction coefficients and the specific wear rates for the a-CN_x/Si₃N₄ tribo-pairs were investigated and analyzed synthetically by ball-on-disk tribometer. The worn surfaces were observed by optical microscope. The results showed that the a-CN_x coatings contained 12 at.% nitrogen, and their structure was a mixture of sp²and sp³ bonds. The a-CN_x coatings’ nanohardness was 29 GPa. The influence of sliding speed on the friction coefficients and the specific wear rate of the CN_x coatings was more obvious than that of normal load. The friction coefficients and the specific wear rate of the CN_x coatings decreased as the sliding speed increased. At a sliding speed higher than 0.1 m/s, the friction coefficients were less than 0.04. The specific wear rates of the a-CN_x coatings were higher than those of Si₃N₄ balls at a sliding speed below 0.1 m/s, while the specific wear rates of the a-CN_x coatings and the Si₃N₄ balls all fluctuated around a lower level of 10^− 8 mm³/Nm as the sliding speed increased beyond 0.2 m/s. To describe the wear behavior of a-CN_x coatings sliding against Si₃N₄ balls in water with normal loads of 3-15 N and sliding speeds of 0.05-0.5 m/s, the wear-mechanism map for the a-CN_x/Si₃N₄ tribo-pairs in water was developed.     

纳米Si3N4 对TC4钛合金微弧氧化层微观结构和性能的影响

在基电解液中加入氮化硅纳米颗粒,对TC4钛合金进行微弧氧化（MAO）处理,研究了Si₃N₄浓度对微弧氧化层表面形貌、耐蚀性和耐磨性的影响。添加Si₃N₄的MAO层呈现多孔结构,当Si₃N₄浓度为1 g/L时,涂层厚度最大,且经过7 d的酸腐蚀试验,该涂层的耐蚀性良好,腐蚀速率最低,约为0.057 mg·cm^-2·d^-1。随着Si₃N₄的加入,MAO涂层的抗菌性能先升高后降低。当Si₃N₄的添加量为1 g/L时,该MAO层的抗菌性能最好。Si₃N₄的加入能明显提高涂层在模拟海水中的耐磨性。当Si₃N₄的添加量为3和4 g/L时,所得涂层的摩擦系数低且稳定,且添加3 g/L Si₃N₄制备来的MAO涂层表现出优异的耐磨性。     

Thermal shock behavior of Si3N4-TiN nano-composites

Si₃N₄-TiN nano-composites were fabricated by hot press sintering nano-sized Si₃N₄ and TiN powders. The microstructure, mechanical properties and thermal shock behavior of Si₃N₄-TiN nano-composites were investigated. The addition of proper amount TiN particles can significantly increase the flexural strength and the fracture toughness. Si₃N₄-TiN nano-composites showed both higher critical temperature difference and higher residual strength compared with those of monolithic silicon nitride nano-ceramic when the amount of TiN is less than 15 wt.%. But a further increase in the amount of TiN leaded to a decrease in the thermal shock resistance.     

Synthesis and phosphorescence properties of Mn, La and Ho in MgAl2Si2O8

Mn⁴⁺, La³⁺ and Ho³⁺ doped MgAl₂Si₂O₈-based phosphors were first synthesized by solid state reaction. They were characterized by thermogravimetry (TG), differential thermal analysis (DTA), X-ray powder diffraction (XRD), photoluminescence (PL) and scanning electron microscopy (SEM). The phosphors were obtained at about 1300 °C. They showed broad red and fuchsia-pink emission bands in the range of 610-715 nm and had a different maximum intensity when activated by UV illumination. Such a fuchsia-pink emission can be attributed to the intrinsic d-d transitions of Mn⁴⁺.     

Effects of pelletization of reactants and diluents on the combustion synthesis of Si3N4 powder

Reactants were pelletized, and then combustion synthesis of Si₃N₄ powder was achieved under the N₂ pressure of 3.0 MPa. Effects of the pelletization of reactants and Si₃N₄ diluents on the combustion process parameters and the characteristics of products were studied. The combustion mode of single reactant pellet was preliminarily discussed. The results indicated that the combustion reaction of single pellet was layer-by-layer from the surface to the core, which led to two peaks on the combustion temperature variation waves. With increasing the diluents content, the morphologies of Si₃N₄ particles changed from short rods into equiaxed grains, and residual Si in the final products obviously decreased. Single phase β-Si₃N₄ powder mainly contained equiaxed grains was prepared when 58 wt.% diluents was added.     

Perpendicular magnetic anisotropy in 70 nm CoFe2O4 thin films fabricated on SiO2/Si(1 0 0) by the sol-gel method

Cobalt ferrite CoFe₂O₄ films were fabricated on SiO₂/Si(1 0 0) by the sol-gel method. Films crystallized at/above 600 °C are stoichiometric as expected. With increase of the annealing temperature from 600 °C to 750 °C, the columnar grain size of CoFe₂O₄ film increases from 13 nm to 50 nm, resulting in surface roughness increasing from 0.46 nm to 2.55 nm. Magnetic hysteresis loops in both in-plane and out-of-plane directions, at different annealing temperatures, indicate that the films annealed at 750 °C exhibit obvious perpendicular magnetic anisotropy. Simultaneously, with the annealing temperature increasing from 600 °C to 750 °C, the out of plane coercivity increases from 1 kOe to 2.4 kOe and the corresponding saturation magnetization increases from 200 emu/cm³ to 283 emu/cm³. In addition, all crystallized films exhibit cluster-like structured magnetic domains.     

Annealing temperature effect on the corrosion parameters of autocatalytically produced Ni-P and Ni-P-Al2O3 coatings in artificial seawater

Ni-P and Ni-P-Al₂O₃ amorphous alloy coatings with 9.3 and 8.3 wt.% P respectively were obtained by autocatalytic deposition at 90 °C on carbon steel substrates. The effect of annealing temperature (100, 200, 300, 400 and 500 °C) upon the corrosion parameters of the coatings in artificial seawater with pH 5.0 and 8.1 at room temperature was evaluated by potentiodynamic polarisation and electrochemical impedance spectroscopy. It was found that deposits annealed at 400 and 500 °C presented an increase of the charge transfer resistance and negligible changes on samples annealed at lower temperature. Polarisation tests showed a charge transfer controlled anodic kinetics on both Ni-P and Ni-P-Al₂O₃ deposits and diffusion controlled cathodic reaction in artificial seawater at pH 5.0 and 8.1. The coatings did not present passive behaviour in the electrolytes and impedance measurements showed a single time constant for all cases with the lowest double layer capacitance (C_dl) for samples annealed at 400 and 500 °C. The best corrosion parameters were observed on Ni-P and Ni-P-Al₂O₃ coatings annealed at temperatures higher than 400 °C, which is the temperature where crystallisation of this kind of coatings takes place.     

Cyclic oxidation behavior and thermal barrier effect of YSZ-(Al2O3/YAG) double-layer TBCs prepared by the composite sol-gel method

Novel YSZ (6 wt.% yttria partially stabilized zirconia)-(Al₂O₃/YAG) (alumina-yttrium aluminum garnet, Y₃Al₅O₁₂) double-layer ceramic coatings were fabricated using the composite sol-gel and pressure filtration microwave sintering (PFMS) technologies. The thin Al₂O₃/YAG layer had good adherence with substrate and thick YSZ top layer, which presented the structure of micro-sized YAG particles embedded in nano-sized α-Al₂O₃ film. Cyclic oxidation tests at 1000 °C indicated that they possessed superior properties to resist oxidation of alloy and improve the spallation resistance. The thermal insulation capability tests at 1000 °C and 1100 °C indicate that the 250 μm coating had better thermal barrier effect than that of the 150 μm coating at different cooling gas rates. These beneficial effects should be mainly attributed to that, the oxidation rate of thermal grown oxides (TGO) scale is decreased by the “sealing effect” of α-Al₂O₃, the “reactive element effect”, and the reduced thermal stresses by means of nano/micro composite structure. This double-layer coating can be considered as a promising TBC.     

Oxidation behavior of Al4SiC4 ceramic up to 1700 °C

Isothermal oxidation behavior of Al₄SiC₄ ceramics at the temperature range from 1200 °C to 1700 °C in air for 10-20 h was investigated. The results indicated that this material had an excellent oxidation resistance from 1200 °C to 1600 °C, and the kinetics of oxidation obeyed the parabolic law with an activation energy of 220 ± 20 kJ mol⁻¹. The oxide scales consisted of an outer oxide layer with higher density, a middle oxide layer with a few of large size pores and a reaction layer which is near to the matrix with a number of small size pores over the temperature ranges. A number of pores exist in the middle oxide scale. The oxide surface and cross-sectional morphologies were observed by scanning electron microscope (SEM) technique and the formation mechanism of the oxidation layers was also analyzed.     

Electrochemical performance of magnetron sputter deposited LiFePO4-Ag composite thin film cathodes

LiFePO₄ thin films have been sputtered from a pure LiFePO₄ target onto Ag/SS, Ag/Si₃N₄/Si and Si₃N₄/Si substrates. All of the deposited films were annealed at 973 K for 1 hr in H₂/Ar (5 %) atmosphere. Substrate induced microstructural and crystallographic evolutions have been observed by a scanning electron microscope and X-ray diffraction. Energy dispersion spectra and X-ray photoelectron spectra revealed that Ag was mixed in the LiFePO₄ films deposited on Ag under layers. Ceramic metal composite thin films were obtained. The film conductivity (1 × 10^− 3 Scm^− 1) is therefore elevated by an order of six, compared with pure LiFePO₄ (10^− 9 Scm^− 1). The electrochemical measurements of the LiFePO₄-Ag films showed a flat plateau at 3.4 V (v.s. Li/Li⁺) and a reversible capacity of 80 mAh/g. Optimization of Ag contents may further improve the discharge capacity.     

Coke formation and metal dusting of electroplated Ni3Al-CeO2-based coatings in CO-H2-H2O

Coke formation and metal dusting of electrodeposited pure, 5 μm CeO₂-dispersed, and 9-15 nm CeCO₂-dispersed Ni₃Al coatings were investigated in CO-H₂-H₂O at 650 °C for a period of 500 h. All Ni₃Al coatings showed the inferior long-term resistance to coke formation and metal dusting to the Fe-Ni-Cr alloy due to failure to form a continuous Al₂O₃ scale. CeO₂-dispersed Ni₃Al coatings, especially 9-15 nm CeCO₂-dispersed coatings, exhibited more severe coke formation and metal dusting than the pure Ni₃Al coating. The detrimental effect of CeO₂ is believed to be caused by the enhanced formation of NiO/Ni crystals on the coating surfaces or at the grain boundaries, which catalysed the carbon deposition and promoted the carbon attack on Ni₃Al coatings.     

Microstructure and magnetic properties of HVOF thermally sprayed Fe75Si15B10 coatings

Partially amorphous Fe₇₅Si₁₅B₁₀ coatings were prepared from nanostructured feedstock powders by using high velocity oxy-fuel spraying. Scanning electron microscopy, X-ray diffraction, Vickers indenter and magnetic measurements were used to investigate microstructural, structural, microhardness and magnetic properties of the coatings. The Rietveld refinement of the X-ray diffraction patterns reveals the presence of an amorphous phase, nanocrystalline α-Fe(Si,B) structure having a lattice parameter close to 0.2841 nm and an average crystallite size of about 78-83 nm in addition to small amounts of Fe₃O₄ oxide (104 nm) and Fe₂B boride (151 nm), which disappear completely with increasing coating thickness. Coercivity and microhardness values are 15.5 Oe and 478 Hv, respectively, for 84 μm thickness.     

Oxidation behavior of arc-sprayed FeMnCrAl/Cr3C2-Ni9Al coatings deposited on low-carbon steel substrates

FeMnCr/Cr₃C₂ and FeMnCrAl/Cr₃C₂ coatings, using Ni9Al arc-sprayed coating as an interlayer on low-carbon steel substrates, were deposited by high velocity arc spraying (HVAS) on the cored wires. The high temperature oxidation behavior of the arc-sprayed FeMnCrAl/Cr₃C₂-Ni9Al and FeMnCr/Cr₃C₂ coatings on the low-carbon steel substrates was studied during isothermal exposures to air at 800 °C. The surface and interface morphologies of the coatings after isothermal oxidation after 100 h were observed and characterized by optical microscopy, field emission scanning electron microscope, energy dispersion spectrum, and X-ray diffraction. The results showed that the oxidation weight gains of the coatings were significantly lower than that of the low-carbon steel substrate. Moreover, the FeMnCrAl/Cr₃C₂-Ni9Al coating registered the lowest oxidation rate. This favorable oxidation resistance is due to the Al and Cr contents of the aforementioned coating that inhibits the generation of Fe and Mn oxides. This is attributed to the interdiffusion between the substrates and the Ni9Al arc-sprayed coating, which can convert the mechanical bonding between substrates and coatings into a metallurgical one, thereby inhibiting the oxidation of interface between the low-carbon steel and the coating.     

Photoluminescence and thermoluminescence studies of Mg2SiO4:Eu nano phosphor

Nanoparticles of Eu³⁺ doped Mg₂SiO₄ are prepared using low temperature solution combustion technique with metal nitrate as precursor and urea as fuel. The synthesized samples are calcined at 800 °C for 3 h. The Powder X-ray diffraction (PXRD) patterns of the sample reveled orthorhombic structure with α-phase. The crystallite size using Scherer's formula is found to be in the range 50-60 nm. The effect of Eu³⁺ on the luminescence characteristics of Mg₂SiO₄ is studied and the results are presented here. These phosphors exhibit bright red color upon excitation by 256 nm light and showed the characteristic emission of the Eu³⁺ ions. The electronic transition corresponding to ⁵D₀ → ⁷F₂ of Eu³⁺ ions (612 nm) is stronger than the magnetic dipole transition corresponding to ⁵D₀ → ⁷F₁ of Eu³⁺ ions (590 nm). Thermoluminescence (TL) characteristics of γ-rayed Mg₂SiO₄:Eu³⁺ phosphors are studied. Two prominent and well-resolved TL glows with peaks at 202 °C and 345 °C besides a shoulder with peak at ∼240 °C are observed. The trapping parameters-activation energy (E), order of kinetics (b) and frequency factor (s) are calculated using glow curve shape method and the results obtained are discussed.     

Influence of deposition conditions on mechanical and tribological properties of nanostructured TiN/CNx multilayer films

Nanostructured TiN/CN_x multilayer films were deposited onto Si (100) wafers and M42 high-speed-steel substrates using closed-filed unbalanced magnetron sputtering in which the deposition process was controlled by a closed loop optical emission monitor (OEM) to regulate the flow of N₂ gas. Multilayers with different carbon nitride (CN_x) layer thickness could be attained by varying the C target current (0.5 A to 2.0 A) during the deposition. It was found that the different bilayer thickness periods (i.e. the TiN layer thickness Λ_TiN was fixed at 3.0 nm while the CN_x layer thickness Λ_CNx was varied from 0.3 to 1.2 nm) significantly affected the mechanical and tribological properties of TiN/CN_x multilayer films. These multilayer films were characterized and analyzed by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), atomic force microscopy (AFM), Rockwell-C adhesion test, scratch test, pin-on-disc tribometer, and nanoindentation measurements. XPS analyses revealed that the chemical states, such as TiN, TiC, TiN_xO_y and TiO_2, existed in a TiN layer. Nanoindentation results showed that the hardness was highly dependent on the bilayer thickness. A maximum hardness of ~ 41.0 GPa was observed in a multilayer film at bilayer thickness Λ_TiN = 3.0 nm and Λ_CNx = 0.9 nm. All multilayer films exhibited extreme elasticity with elastic recoveries as high as 80% at 5 mN maximum load. The compressive stresses in the films (in a range of 1.5-3.0 GPa) were strongly related to their microstructure, which depended mainly on the incorporation of nitrogen in the films. By scratch and Rockwell-C adhesion tests, the multilayer films with smaller bilayer thicknesses (Λ_TiN = 3.0 nm, Λ_CNx = 0.3 and 0.6 nm) exhibited the best adhesion and cohesive strength. The critical load value obtained was as high as ~ 78 N for the films with Λ_TiN = 3.0 nm, Λ_CNx = 0.9 nm. The friction coefficient value for a multilayer at Λ_TiN = 3.0 nm and Λ_CNx = 0.9 nm was found to be low 0.11. These adhesive properties and wear performance are also discussed on the basis of microstructure, mechanical properties and tribochemical wear mechanisms.     

Effect of applied current on the electrodeposited Ni-Al2O3 composite coatings

Nano-sized Al₂O₃ ceramic particles (50 nm) were co-deposited with nickel using electrodeposition technique to develop composite coatings. The coatings were produced in an aqueous nickel bath at different current densities and the research investigated the effect of applied current on microstructure and thickness of the coatings. The variation in some mechanical properties such as hardness, wear resistance, and the adhesive strength of the composite coatings is influenced by the applied current and this was also studied. The morphology of the coatings was characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy. The hardness, wear resistance, and bond strength of the coatings were evaluated by Vickers micro-hardness test, pin-on-disc test, and tensile test, respectively. Results showed that the Al₂O₃ particles were uniformly distributed in the coatings, and the coatings deposited at a current density of 0.01 A/cm² was most favorable in achieving a maximum current efficiency which causes the co-deposition of a maximum amount of Al₂O₃ particles (4.3 wt.%) in the coatings. The increase in Al₂O₃ particles in the coatings increased the mechanical properties of the Ni-Al₂O₃ composite coatings by grain refining and dispersion strengthening mechanisms.     

Hot corrosion behaviour of plasma sprayed YSZ/Al2O3 dispersed NiCrAlY coatings on Inconel-718 superalloy

Oxide dispersed NiCrAlY bond coatings have been developed for enhancing thermal life cycles of thermal barrier coatings (TBCs). However, the role of dispersed oxides on high temperature corrosion, in particular hot corrosion, has not been sufficiently studied. Therefore, the present study aims to improve the understanding of the effect of YSZ dispersion on the hot corrosion behaviour of NiCrAlY bond coat. For this, NiCrAlY, NiCrAlY + 25 wt.% YSZ, NiCrAlY + 50 wt.% YSZ and NiCrAlY + 75 wt.% YSZ were deposited onto Inconel-718 using the air plasma spraying (APS) process. Hot corrosion studies were conducted at 800 °C on these coatings after covering them with a 1:1 weight ratio of Na₂SO₄ and V₂O₅ salt film. Hot corrosion kinetics were determined by measuring the weight gain of the specimens at regular intervals for a duration of 51 h. X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy techniques were used to determine the nature of phases formed, examine the surface attack and to carry out microanalysis of the hot corroded coatings respectively. The results show that YSZ dispersion causes enhanced hot corrosion of the NiCrAlY coating. Leaching of yttria leads not only to the formation of the YVO₄ phase but also the destabilization of the YSZ by hot corrosion. For the sake of comparison, the hot corrosion behaviour of a NiCrAlY + 25 wt.% Al₂O₃ coating was also examined. The study shows that the alumina dispersed NiCrAlY bond coat offers better hot corrosion resistance than the YSZ dispersed NiCrAlY bond coat, although it is also inferior compared to the plain NiCrAlY bond coat.