W.J. Meng

Microstructure and mechanical properties of Ti–Si–N coatings

A series of Ti-Si-N coatings with 0 < Si < 20 at.% were synthesized by inductively coupled plasma assisted vapor deposition. Coating composition, structure, atomic short-range order, and mechanical response were characterized by Rutherford backscattering spectrometry, transmission electron microscopy, x-ray absorption near-edge structure spectroscopy, and instrumented nanoindentation. These experiments show that the present series of Ti-Si-N coatings consists of a mixture of nanocrystalline titanium nitride (TiN) and amorphous silicon nitride (a-Si:N); i.e., they are TiN/a-Si:N ceramic/ceramic nanocomposites. The hardness of the present series of coatings was found to be less than 32 GPa and to vary smoothly with the Si composition.

Structure and mechanical properties of Ti-Si-N ceramic nanocomposite coatings

Abstract We have synthesized a series of Ti–Si–N coatings with 0–20 at.% Si by high-density plasma-assisted vapor phase deposition. Composition, structure and atomic short-range order were characterized by Rutherford backscattering spectrometry (RBS), transmission electron microscopy (TEM), θ–2θ X-ray diffraction (XRD) and X-ray absorption near-edge structure (XANES) spectroscopy. The mechanical properties of these coatings were characterized by instrumented nanoindentation and compared to those of B1-TiN. Our experiments show that the present series of Ti–Si–N coatings are nanocomposites, consisting of a nm-scale mixture of crystalline titanium nitride (TiN) and amorphous silicon nitride (a-Si:N). The hardness of the present series of Ti–Si–N coatings was found to be less than 32 GPa.

Fabrication of copper-based microchannel devices and analysis of their flow and heat transfer characteristics

Metal-based microchannel heat exchangers (MHEs) offer potential solutions to high heat flux removal applications, such as cooling of high-performance microelectronic and energy-efficient lighting modules. Efficient fabrication of metal-based MHEs and quantitative flow and heat transfer measurements on them are critical for establishing the economic and technical feasibility of such devices. In this paper, all-Cu MHE prototypes were fabricated. Results of flow and heat transfer testing made on these Cu-based MHE prototypes are reported. Efficient fabrication of Cu-based high-aspect-ratio microscale structures (HARMSs) was achieved through direct molding replication using surface-engineered metallic mold inserts. Replicated Cu HARMSs were assembled through solid-state bonding to form all-Cu MHE prototypes. Flow and heat transfer testing of the Cu MHE prototypes was conducted to determine the average rate of heat transfer from the solid Cu body to water flowing within the enclosed microchannel array. Experimentally observed flow and heat transfer data are analyzed and shown to agree with known macroscale correlations once surface roughness and entrance length effects are taken into account.

Stresses during micromolding of metals at elevated temperatures: pilot experiments and a simple model

The Lithographie, Galvanoformung, Abformung (LIGA) technique is important for making metal-based high-aspect-ratio microscale structures (HARMS) and microdevices derived from metal-based HARMS. Recently, molding replication of HARMS made of Pb, Zn, and Al has been demonstrated, advancing LIGA technology from the state where only polymer-based HARMS could be replicated by molding. This demonstration offers a potential means for economical fabrication of a wide variety of metal-based microdevices. Micromolding of a metal requires heating the metal to be molded to a significant fraction of its melting temperature. At high temperatures, the strength of the mold insert itself will typically decrease. The insert strength thus places a limit on the range of materials that can be molded. In this paper, micromolding and tensile experiments on Pb were carried out. A simple mechanics model of the micromolding process was developed. This model relates the stresses on the insert during micromolding primarily to the yield strength of the molded metal and frictional tractions on the sides of the insert. Reasonable agreement was obtained between the Pb experiments and the model predictions. Ramifications for other material systems are discussed.

Structure of vapor-phase deposited Al-Ge thin films and Al-Ge intermediate layer bonding of Al-based microchannel structures

Al-based high-aspect-ratio microscale structures (HARMS) are basic building blocks for all-Al microdevices. Bonding of Al-based HARMS is essential for device assembly. In this paper, bonding of Al-based HARMS to flat Al plates using Al-Ge thin film intermediate layers is investigated. The structure of sputter codeposited Al-Ge thin films was studied by high-resolution transmission electron microscopy as a function of the average film composition. The structure of the interface region between Al-based HARMS bonded to flat Al plates is studied by combining focused ion beam sectioning and scanning electron microscopy. An extended bonding interface region, {approx}100 {micro}m in width, is observed and suggested to result from liquidus/solidus reactions as well as diffusion of Ge in solid Al at the bonding temperature of 500 C. The extended interface region is suggested to be beneficial to Al-Al bonding via Al-Ge intermediate layers.

Characterization of high temperature deposited Ti-containing hydrogenated carbon thin films

A detailed structural and mechanical characterization was performed on Ti-containing hydrogenated amorphous carbon (Ti-C:H) thin films deposited at ∼600°C by plasma assisted hybrid chemical/physical vapor deposition. The structural and mechanical characteristics of these specimens were compared to those deposited at the lower temperature of ∼250°C. The results indicated that Ti-C:H consisted of a nanocrystalline TiC phase and a hydrogenated amorphous carbon (a-C:H) phase, and that Ti atoms were incorporated into Ti-C:H predominantly as B1-TiC. Deposition at ∼600°C promoted TiC precipitation, resulting in little Ti dissolution within the a-C:H matrix. High temperature deposited Ti-C:H specimens were found to possess lower modulus and hardness values as compared to low temperature deposited specimens, especially at low Ti compositions. This is rationalized by electron microscopy evidence of increased short and medium range graphitic order within the a-C:H matrix of high temperature deposited Ti-C:H, and sup...

Structure and Mechanical Properties of Ceramic Nanocomposite Coatings

Current research on ceramic nanocomposite coatings is reviewed, with emphasis placed on recent developments in two-phase ceramic nanocomposites. Results on the structure, mechanical properties, and tribological characteristics of Ti-C:H and Ti-Si-N coatings are highlighted. Potential applications of ceramic nanocomposite coatings to surface engineering of macro- and micro- scale mechanical systems are discussed.