Evaluation of capabilities of the nanoindentation test in the determination of flow stress characteristics of the matrix material in porous sinters

Herein, we evaluate the nanoindentation test capabilities in the determination of flow stress characteristics of the matrix material in porous sinters. The Distaloy AB sample with 15% porosity after the sintering operation is selected as a case study for the investigation. 2D and 3D imaging techniques are employed first to highlight difficulties in identifying reliable nano hardness measurement zones for further properties evaluation. Then, nanoindentation test results are acquired with Berkovich tip pressed under various loads at different locations in the sample. Systematic indentations in the quartz sample are used as a cleaning procedure to minimize the effect of the possible build-up around the indenter tip. The representative indentation load range is selected based on the extracted material characteristics. With that, the stress–strain response of the sinter matrix material is identified. The reliability of the determined flow stress curve is confirmed with the use of conical nanoindentation measurement results and finite element simulations. Obtained results show that it is possible to calculate reliable flow stress characteristics of the matrix in the porous samples, with the assumption that experiments under various loading conditions and from various locations in the matrix are performed. It is also pointed out that various indentation loads should be used to eliminate the influence of the pile-up or scale effects that affect the overall material response.

Effects of Annealing on Enthalpy Recovery and Nanomechanical Behaviors of a La-Based Bulk Metallic Glass

Structural relaxation and nanomechanical behaviors of La65Al14Ni5Co5Cu9.2Ag1.8 bulk metallic glass (BMG) with a low glass transition temperature during annealing have been investigated by calorimetry and nanoindentation measurement. The enthalpy release of this metallic glass is deduced by annealing near glass transition. When annealed below glass transition temperature for 5 min, the recovered enthalpy increases with annealing temperature and reaches the maximum value at 403 K. After annealed in supercooled liquid region, the recovered enthalpy obviously decreases. For a given annealing at 393 K, the relaxation behaviors of La-based BMG can be well described by the Kohlrausch-Williams-Watts (KWW) function. The hardness, Young’s modulus, and serrated flow are sensitive to structural relaxation of this metallic glass, which can be well explained by the theory of solid-like region and liquid-like region. The decrease of ductility and the enhancement of homogeneity can be ascribed to the transformation from liquid-like region into solid-like region and the reduction of the shear transition zone (STZ).

Effects of annealing on phase structure and magnetic characteristics of sputter deposited Ni2FeGa/Si (100) thin films

This paper investigates the effects of post-deposition annealing on the evolution of phase structure and magnetic properties of magnetron sputtered Ni2FeGa/Si (001) thin films. The results revealed that the as-deposited film was partially crystallized in an fcc structure, i.e. [Formula: see text] phase. Crystallization of the amorphous structure into the [Formula: see text] phase was greatly encouraged following annealing at 723 K for 1 h. Annealing at higher temperatures for the same period triggered the formation of the bcc austenitic phase, which competed with the [Formula: see text] phase simultaneously for crystallization and grain growth. The evolution of phase structure and grain size also influenced the nanomechanical properties of the films according to the nanoindentation measurement. The film annealed at 873 K for 1 h showed high hardness and elastic modulus values of 11.1 GPa and 156 GPa. The [Formula: see text] phase showed stronger ferromagnetic characteristics relative to the bcc austenite due to the richer Fe content. This leads to the saturation magnetization to be maximized at 80 emu/g when annealed at 773 K for 1 h attributed to the enhanced film crystallinity and dominant volume fraction of [Formula: see text] phase in the thin film.

Influence of Post-Annealing on the Structural and Nanomechanical Properties of Co Thin Films

The correlations between the microstructure and nanomechanical properties of a series of thermal annealed Co thin films were investigated. The Co thin films were deposited on glass substrates using a magnetron sputtering system at ambient conditions followed by subsequent annealing conducted at various temperatures ranging from 300 °C to 800 °C. The XRD results indicated that for annealing temperature in the ranged from 300 °C to 500 °C, the Co thin films were of single hexagonal close-packed (hcp) phase. Nevertheless, the coexistence of hcp-Co (002) and face-centered cubic (fcc-Co (111)) phases was evidently observed for films annealed at 600 °C. Further increasing the annealing temperature to 700 °C and 800 °C, the films evidently turned into fcc-Co (111). Moreover, significant variations in the hardness and Young’s modulus are observed by continuous stiffness nanoindentation measurement for films annealed at different temperatures. The correlations between structures and properties are discussed.

Research of Diamond-Like Carbon Film Deposited by Double Pulsed Lasers

In the research of Diamond-like carbon (DLC) Film deposited by pulsed laser, method of double pulsed laser deposition was presented. Ti:Sapphire (800nm, 120fs) laser and KrF (248nm, 20ns) laser were used orderly to ablate graphite target. Through controlling parameters of two laser beams, double-layer DLC film was deposited on silicon substrate. The hardness and inner-stress of the DLC film changed gradually from substrate to atmosphere-interface. Nanoindentation measurement system and fourier transfer infrared spectrograph were used to hardness and transmittance of the film. Meanwhile, adhesive tape, 9.8N rubber, NaOH liquor and boiling water were used to compare the adhesion and environment adaptability of double layer or monolayer DLC film samples qualitatively. Results showed that DLC film deposited by double beam pulsed laser not only had high transmittance and hardness, but also kept well and had no phenomenon of peeling off after the tests including dipped in boiled water, etc. Compared to DLC films deposited by single pulsed laser, the chemical and thermal inertness of the double-layer DLC film deposited by double pulsed lasers was much better.