Plasma sprayed calcium phosphate coatings on Ti(alloy) have been considered advantageous over the uncoated Ti as dental implants or orthopedic prostheses due to their abilities to decrease healing time, attach firmer to the bone, and inhibit ion release from the Ti substrate. However, the coating was found not to adhere well to the Ti substrate, presumably because there is no or little chemical bonding between the calcium phosphate coating and the Ti substrate. The interfacial bond strength relies almost entirely on the mechanical locking of calcium phosphate splats onto the roughened Ti surface. In this study, the interfacial area between the calcium phosphate coating and the Ti-6A1–4V substrate was characterized using SEM and TEM. The results revealed the presence of amorphous calcium phosphate layer at the interface, which is believed to be responsible for the low bond strength. Also small particles were observed which were embedded in the amorphous phase near the interface. The presence of the amorphous phases is very important since they are more easily attacked by the physiological solution than crystalline phases are.

Evidence for the formation of a passive layer between a conductive polymer coating and aluminum alloy surfaces is reported Experimental results from electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) on aluminum alloys coated with a novel double strand conductive polymer coating based on polyaniline reveal the evidence for the formation of passive layer. The key results are: (1) Modeling of EIS data is best fit with a three RC circuit, indicating a third interface between the polymer coating and the alloy's surface; (2) EIS testing in acidic salt solutions shows the conductive polymer coating performs differently and better than a typical anodized or chromáte conversion coating indicating a possibly different interface layer than a typical aluminum oxide and (3) SEM studies of the aluminum surface, after the polymer film is removed, indicates that this interfacial layer has a dense and smooth “oxide type” surface morphology. The experimental results are consistent with a mechanism in which the conducting polymer serves as a surface conversion agent that oxidizes the aluminum metal surface to form a passive layer.

Boron nitride thin films have been produced on silicon carbide whiskers (SiCw) by a novel processing method. A polydivinylbenzene (PDVB) coating was formed in situ on the whisker surface which was subsequently thermally degraded creating a highly porous carbon layer. The total available pore volume of the carbon layer/ SiCw system (SiCwC) was varied by controlling the quantity of PDVB adsorbed. Next, anhydrous sodium borate was mixed with the SiCwC, and upon heating, the precursor melted and absorbed into the porous carbon layer followed by nitridation with anhydrous ammonia. Under certain reaction conditions, silicon oxynitride was also produced as a sublayer. The amount of the latter can be controlled by varying the reaction temperature and time. Control over the thickness of the BN film was achieved by varying the amount of the carbonized polymer layer in proportion to the quantity of sodium borate.

Highly oriented diamond films were deposited on a (001) silicon substrate by bias enhanced MPCVD technique. Three-dimensional TEM characterizations were carried out to understand the nucleation and growth mechanism of diamond grains. The surface morphology, defects, and misorientations of diamond films were compared as a function of synthesizing temperatures and thickness of the films. From our experimental results the texture formation mechanism of diamond films is discussed.

Synthesis and characterization of titanium and zirconium oxide and carbide thin films (1–25 μm) on spherical substrates is reported. Hydrolysis of an appropriate metal alkoxide precursor in aqueous acid yields the amorphous metal oxide coating. Thermal treatment can produce the highly crystalline phases of the oxides or, in the presence of a carbon containing reducing gas, the metal carbide. Scanning electron microscopy and x-ray diffraction have been used to study the surface morphology and the crystallographic structure of the coating films. Morphological characteristics strongly depend on the acid species and acid strength used during hydrolysis. The thickness of the film is also governed by control of the acid hydrolysis step.

Cubic boron nitride films were prepared by helicon wave plasma CVD process on (100) Si. The growth and delamination mechanism of c-BN film was investigated with FT-IR spectroscopy and transmission electron microscopy. The film deposited under the intense impact of energetic ions is usually delaminated from the substrate after deposition. It is found that moisture in the air, surface roughness of the film and substrate, as well as severe compressive stresses in the film are the primary contributors to film delamination. An aqueous oxidation was verified by EDXS analysis, which generate local stress by volume expansion at the crack region in the c-BN layer. From the experimental results and ??? observation a model for the delamination mechanism of c-BN film is suggested. Based on the delamination mechanism, several kinds of remedies such as post annealing and post N2 plasma treatment were carried out for improving the adhesion.

Semiconducting TiO2 has some photoelectrochemical reactions under ultra-violet irradiation. These photoelectrochemical behaviors studied as possible protection from corrosion. TiO2 thick films were prepared on stainless steel by plasma-spray coating. The film thicknesses were 50∼100μm. The films were characterized by X-ray diffraction, and the diffraction patterns clearly showed a rutile type structure. The crystallization of the films depends on the spray coating conditions. We have investigated the protection properties of the films by measuring the electrode potential. The electrode potential of the films were reduced by about 250m V under ultra-violet irradiation. This potential drop value is sufficient for protection from the corrosion.

In this study, continuous microscratch testing was used to determine the effects of compressive residual stresses on the fracture of thin tantalum nitride films. The films were sputter deposited at room temperature onto single crystal sapphire substrates to a thickness of 600 nm. Some films were left in the as-deposited condition while the remaining films were vacuum annealed at 300°C. The only discernible change in structure was a surface rearrangement of atoms into parallel arrays of striations on the vacuum annealed samples revealing a high compressive residual stress in the films. These stresses had a strong effect on fracture as shown by the as-deposited films which buckled readily during scratch tests forming uniform-width and circular blisters while the vacuum annealed films exhibited a much lower susceptibility to fracture. Application of mechanics-based models for film buckling defined the levels of compressive residual stress and their effect on interfacial fracture.

Residual stresses were measured in different types of diamond coatings deposited onto molybdenum substrates by hot filament chemical vapor deposition. The types of coatings examined include a continuous single layer diamond coating and a continuous multilayer diamond composite coating with an aluminum nitride embedding layer. The stresses were determined by X-ray diffraction and Raman spectroscopy and compared.

One of the key factors affecting the long-term reliability of thin film structures in microelectronics devices is the fracture resistance of their interfaces. Of the many different interfaces formed during device fabrication, the SiO2/TiN interface is amongst the most common. In order to measure the fracture energy of this interface, we have been utilizing a test in which a narrow strip of a material, having a large intrinsic tensile stress, is deposited and lithographically defined onto the SiO2/TiN/Al thin film structure. The elastic strain energy in the micro-strip provides an additional driving force to debond the weakest interface in the structure. Decohesion occurs when the thickness of the micro-strip, and hence the total elastic strain energy, exceeds a critical value. Another measure of the fracture resistance in the same test is the length of the strip that remains intact after debonding at both ends. This is a function of the intrinsic stress, the thickness of the superlayer, and the modulus ratios. In addition to presenting results on the measured fracture energy of the SiO2/TiN interface, evidence for stress-corrosion will be described.

Mechanical response of interfaces between intermetallic matrices and ductile reinforcements is of considerable interest in intermetallic matrix composite design. A new approach has been developed to study crack initiation at a planar bimaterial interface by loading one of the adjoining phases in compression. A primarily Mode II stress state with different degrees of superimposed tensile and compressive loading develops at the interface as predicted by FEM analysis. This test method has been used to study NiAl/Mo and NiAl/Cr interfaces in model laminates.

Six types of oxide laminates consisting of combinations of xenotime (YPO4) with zirconia (ZrO2), monazite (LaPO4) with ZrO2, and aluminum orthophosphate (AlPO4) with alumina (Al2O3) were studied. They were fabricated by repeatedly stacking two or three kinds of tape-cast layers, lamination, organic burnout and consolidation by hot-pressing. Two of the YPO4-containing ZrO2 laminates were stacked in a YPO4/yttria-stabilized ZrO2 (Y-ZrO2)/30 vol% Y-ZrO2-70 vol% Al2O3(YZ3-A7)/Y-ZrO2 sequence and in a YPO4/Y-ZrO2 sequence. High strength (∼360 MPa) and apparent work-of-fracture (WOF = ∼ 8.2 kJ/m2) were measured in the first laminate. This oxide laminate demonstrates high damage-tolerance without loss of strength. Both properties were comparable with those of non-oxide laminates. There was an approximately 200-fold increase in WOF, as compared with pure Al2O3. A toughening mechanism by means of the residual, interlaminar shear stress-enhanced, interface delamination is proposed for these good results. Two of the LaP04-containing ZrO2 laminates were fabricated in a LaPO4/70 vol% doped ZrO2-30 vol% Al2O3 stacking sequence and in a LaPO4/Y-ZrO2 sequence. Another two of the AlPO4-containing Al2O3 laminates are fabricated in an AlPO4/Al2O3 and in a (50 vol% AlPO4-50 vol% Al2O3)/Al2O3 stacking sequence. The fracture behavior of these multilayered laminates was also studied. The different results among the three kinds of laminates are discussed.

A novel coating architecture is being examined for enhancing the high temperature, oxidation resistance of molybdenum. The coating incorporates a thin, composite film of MoSi2+1.96 mole fraction SiC in order to match the coefficients of thermal expansion between the molybdenum substrate and the coating. Since the as-deposited composite film is amorphous in nature, a diffusion anneal treatment is carried out at 1000°C to achieve crystallization of the film. In this paper, a detailed examination of the Mo-MoSi2+1.96 SiC interface will be presented. The microstructural features of the composite films will be discussed based on electron microscopy, auger electron spectroscopy (AES), and X-ray diffraction analysis. Finally, a novel diffusion barrier layer for minimizing silicon and carbon diffusion from the coating to the substrate will be discussed.

The mechanisms of the sputter-induced orientation change in YBa2Cu3O7-x(YBCO) films grown on MgO (001) substrates by pulsed organometallic beam epitaxy (POMBE) are investigated by x-ray diffraction, Rutherford backscatter spectroscopy (RBS), cross-section TEM (XTEM) and microanalysis. It is found that the W atom implantation concurring with the ion sputtering plays an important role in effecting the orientation change. This implantation changes the surface structure of the substrate and induces an intermediate layer in the initial growth of the YBCO film, which in turn acts as a template that induces the orientation change. It seems that the surface morphology change caused by ion sputtering has only a minor effect on the orientation change.