Syamal K. Ghosh

Study of the relative wear and abrasion resistance of Ti(C,N) and TiN coatings

Abstract Titanium carbonitride [Ti(C,N)] and titanium nitride (TiN) coatings deposited on AISI 440C stainless steel were characterized for resistance to wear and abrasion. The hardness of the coatings as a function of indentation load was determined using a microhardness testing technique. Wear resistance was measured using a reciprocating ball-on-plane test using a hardened 440C stainless steel ball rider. Wear resistance was also measured using ASTM designation G83-83, a crossed-cylinder metal-to-metal test. The abrasion resistance was determined in a loop tester in which abrasive film configured in a continuous loop was abraded against the coatings. It was determined that the Ti(C,N) coating is harder than the TiN coating. The abrasion test demonstrates that the abrasion resistance of Ti(C,N) coating is superior to that of TiN, but the coating versus metal wear resistance is dependent upon the experimental conditions.

Using morphological changes to make piezoelectric transducers

A method of forming a piezoelectric element which includes piezoelectric material having a variable functionally gradient d-coefficient including coating a block having a uniform concentration of piezoelectric material with a predetermined porosity by applying a first layer having piezoelectric material with a same or different chemical composition than the block onto a surface of the block and having a different porosity than the predetermined porosity which is selected so as to provide a different morphological structure than the block; applying a subsequent layer of piezoelectric material on the first layer with the same or different chemical composition of piezoelectric material than the block and having a different porosity than the previously deposited layer so as to provide a different morphological structure than the block or the previously applied layer(s); applying heat to the block and the applied layer to dry the applied layer; and then applying heat to sinter the piezoelectric block and applied layer so as to form a piezoelectric element with a functionally gradient d-coefficient.

Wear‐induced phase transformation in yttria stabilized zirconia: X‐ray photoelectron spectroscopic studies

X‐ray photoelectron spectroscopy has been used to study near‐surface phase transformation in yttria stabilized zirconia subjected to sliding wear. Characteristic differences are observed in the valence bands of the tetragonal and the monoclinic phases of zirconia. These valence bands have been used as ‘‘fingerprints’’ to monitor phase transformation during wear under different loading conditions. Conventional and glancing angle x‐ray diffraction techniques were found inadequate to detect this phase transformation.

Surface modification and wear characteristics of yttria-doped zirconia

Abstract Surfaces of yttria-stabilized zirconia were modified either by doping with magnesia during sintering or by inducing compressive stress by grinding and polishing. This modification changed the crystal structure of yttria-stabilized zirconia either from tetragonal to cubic or from tetragonal to monoclinic. These surface modifications also resulted in a harder outer surface of yttria-stabilized zirconia without jeopardizing the toughness of the bulk tetragonal phase. The significant improvements in both adhesive and abrasive wear behaviors of tetragonal zirconia ceramic with surfaces having cubic and monoclinic structures are demonstrated.

X-ray photoelectron spectroscopic studies on ceramic composites containing yttria-stabilized zirconia and alumina

Abstract X-ray photoelectron spectroscopy has been used to characterize the surfaces of ceramic composites containing yttria-stabilized zirconia and α-alumina. One of the surfaces of the composite was modified by magnesia diffusion for improved wear resistance. Formation of a magnesia-alumina spinel was detected at the modified surface. Significant shifts in the binding energy of Al2p and O 1s core levels were observed for the modified and the unmodified surface. These were compared with the core levels of standard spinel and sapphire. Auger parameters for several elements were measured for the modified and the unmodified surface as well as the standards. These parameters provided useful information regarding cation-anion coordination in the oxides and assisted in identifying an impurity phase. Valence-band spectra were obtained from the various surfaces under study. These spectra were utilized in a semiquantitative way to characterize the different phases present on the surface of the composite.

Binder coagulation casting of ferroelectric components

Abstract Binder coagulation casting (BCC) is a novel method for near-net shape forming of ferroelectric components with complex geometry or intricate surface features. The process uses low concentrations of nontoxic polymeric binders in an aqueous system to form a low-viscosity slurry, which can be cast in a nonporous mold and coagulated under controlled conditions. This paper highlights an application of BCC technique in prototype manufacturing of a PZT piezoelectric actuator.

Dopant incorporation in ceramics prepared by binder coagulation casting

Uniform incorporation of inorganic dopants and sintering aids into ceramic green bodies is necessary for the development of controlled microstructures during sintering. Binder coagulation casting (BCC) is a novel near-net shape fabrication process that is driven by controlled adsorption of polymeric binders. Two methods were used to incorporate small amounts of inorganic additives into ceramic compositions formed using BCC: the conventional mixed powder method and a novel method of using the organic additive system in BCC as a chelating agent for dopant cations. Cobalt dopant in zirconia was used as a model system for this work. MgO sintering aid in alumina was also examined. Sintering behavior and microstructure analysis using AFM are discussed.

Incipient flocculation molding: A new ceramic forming technique

Abstract Incipient Flocculation Molding (IFM) is a new and low-cost net-shape forming technique for ceramic components. Unlike other ceramic forming processes, the slurry has a very low viscosity, which facilitates molding very intricate features. IFM utilizes a concentrated, non-aqueous, sterically stabilized ceramic colloidal suspension that is injected into a nonporous mold at a very low pressure. As the temperature of the suspension is lowered below the theta-point of the stabilizer-solvent system, it is destabilized, resulting in flocculation of the slurry to a solid mass. The flocculation process is both rapid and reversible. IFM operates essentially as a temperature-dependent deflocculant. IFM is ideal for molding ferroelectric ceramics, particularly PZT powders, for manufacturing actuators having complex and intricate features. This is accomplished by dispersing the powders in a solvent, stabilized by grafted polyethylene glycol (PEG), and injecting into a mold. The solvent is removed by vacuum ev...