Correlations between microstructure, fracture morphology, and fracture toughness of nanocrystalline Ni–W alloys

Abstract

Ni-23at%W thin films were ion-beam machined and tested in bending. Microstructures were characterized with aberration-corrected electron microscopy and the fracture surfaces were inspected after each test with SEM. Nominally amorphous films fractured along oxide streaks that formed during deposition. Heat treating at 700 °C crystallized the samples to a grain size of 30 nm, and the corresponding fracture toughness increased from 2.1 to 2.5 MPa√ . This work demonstrates that mesoscale features and impurities influence amorphous and nanocrystalline Ni-W fracture.Nanocrystalline metals formed from alloys such as Ni-W often offer attractive mechanical properties such as high hardness, but high strength is frequently accompanied by poor fracture toughness [1]. Unfortunately, reliable toughness information is limited because the small number of publications that report on the fracture of nanocrystalline metals indicate (1) that quantitative toughness measurements are challenging to conduct [2], and (2) that the toughness and fracture morphology may be functions not only of composition, pore size, and grain size, but also of mesoscopic features such as nanograin colony size [3]. Quantitatively determining fracture toughness of nanocrystalline metals remains a particular challenge because many such materials are thin films [4,5]. Conventional macro-scale tensile tests or hardness indentation measurements are generally neither feasible nor effective [6]. Likewise, analysis of structure and chemistry at a level sufficient to provide a complete description of the fracture process may require specialized characterization tools that are not widely available. As a result, very few studies have successfully conducted quantitative fracture toughness evaluation with detailed analysis of the links between toughness, microstructure, nanostructure, and localized chemistry.Micro-scale cantilever beam testing provides one viable approach to quantitative toughness measurement [7,8]. It allows the isolation of a nanocrystalline thin film from its substrate and the selection of small defect-free regions to avoid large cracks or pores. In addition, proper selection of specimen preparation and testing conditions allows the use of linear © 2015. This manuscript version is made available under the Elsevier user license

In-depth characterization of as-deposited and annealed Fe-W coatings electrodeposited from glycolate-citrate plating bath

“…In Table 1, the chemical composition of the different samples measured by EDS on the sample surfaces is reported. Electrodeposited tungsten alloys normally contain some oxygen that is incorporated in form of oxides mainly in the top surface layer [13] but also within the coating, forming tungsten oxide streaks [18,41]. As it is seen from Table 1, there is no direct correlation between the Wand O content in the alloy (as well as there is no clear influence of the deposition conditions).…”

The Impact of Pore Structure on Kerogen Geomechanics

“…Hence, the models developed are vulnerable to a high level of discrepancy when applied to other samples with different mineralogical distributions [25]. Micromechanical testing methods such as quasistatic nanoindentation, mapping by nanoindentation, and atomic force microscope AFM have been employed to study variations in mechanical properties, with shale matrices revealing highly heterogeneous behaviors of feldsbar, carbonate, quarts, and organic matter [26][27][28][29][30][31][32][33][34]. Young's modulus of inorganic inclusions is in the range of 50 GPa, while it is less than 10 GPa for organic matter [27][28][29].…”

Lattice Strain Evolutions in Ni-W Alloys during a Tensile Test Combined with Synchrotron X-ray Diffraction

“…These alloys are generally produced by electrodeposition (ED) [ 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 ], magnetron co-sputtering [ 18 ], mechanical alloying [ 19 ], sintering processes [ 1 , 7 ], and thermal plasma-processes [ 20 ]. Due to diffusion of the body-centered cubic (bcc) tungsten phase (W) in the face-centered cubic (fcc) nickel one (Ni), a Ni(W) solid solution is commonly obtained by such processes [ 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 ]. The dissolution of tungsten atoms in the nickel lattice causes a shift of the fcc Bragg peaks towards lower scattering angles [ 7 , 13 , 19 , 22 , 23 ].…”