Operational control of the strength of safety parts limiting ultimate loads

A non-destructive method for determining the shear strength of parts based on the laws of elastoplastic penetration of an indenter into a test material is considered. Experiments confirmed the effectiveness of the method in practice. Keywords: non-destructive method, shear strength, elastoplastic contact, plastic hardness. [email protected]

Contact stiffness of mating surfaces of parts under dynamic loading

The dependences of the relative real contact area of the flat contacting surfaces of steel parts on the nominal pressure under dynamic contact loading are studied. It is determined, that the real contact area under dynamic loading is less than under static one. Keywords dynamic plastic hardness, contact approach, real contact area, contact stiffness. [email protected]

Energy Approach to Material Hardness Determination

Energy hardness is defined as energy density of material plastic displacement from the initial surface level. It is convenient to determine it from the kinetic indentation diagram constructed in the coordinates , where is a relative load, is a relative penetration of a spherical indenter. It dhould be note that a relative energy density is equal to multiplied by the parameter where varies within a narrow range for constructional materials used in machine building. A mean relative error in finding energy hardness by this approach does not exceed 5%. It is shown that for the majority of mechanical engineering materials energy hardness is intermediate between plastic hardness and Meyer’s hardness.

Oxidation Resistance and Self Hardening of CrAlN/BN Nanocomposite Coatings

CrAlN/BN nanocomposite coatings were deposited on mirror-polished silicon wafer and high-speed steel (HSS) substrates using reactive cosputtering, i.e., pulsed dc and rf sputtering of CrAl and h-BN targets, respectively. Further, the oxidation resistance of the obtained coatings was investigated. The CrAlN/BN coating exhibited superior oxidation resistance properties when compared with those of the CrAlN coatings; after annealing the sample at 800 °C in air for 1 h, the plastic hardness value of the CrAlN coatings decreased to 50% of the as-deposited hardness value; in contrast, the CrAlN/BN coatings exhibited self-hardening phenomena from 700 to 800 °C in the range of 5 to 30%. In particular, the CrAlN/18 vol% BN coatings showed an increase of approximately 30% in hardness values, and a maximum hardness value of approximately 50 GPa was reached after annealing the sample at 800 °C in air. The plastic hardness value hardly changed when the sample was annealed up to 800 °C in nitrogen and argon; this result was contrary to the result obtained for the sample that was annealed in air. The radiofrequency glow discharge optical emission spectroscopy (rf-GD-OES) analysis of the CrAlN/18 vol% BN coating annealed in air revealed that the coating has an oxide layer deposited on the surface to a depth of ~200 nm. Conventional transmission electron microscopy (TEM) observations of the same coating indicate that the columnar structure was disrupted by a thin layer (30–40 nm) of the coating annealed in air. The indentation hardness value of the annealed coating was measured using Ar ion sputtering before and after etching of the annealed surface. Subsequently, when the oxide layer was etched to a depth of 200 nm from the surface, the hardness value decreased from approximately 48 GPa to 43 GPa; this result was similar to the results obtained for the as-deposited coating.

Microstructure and Mechanical Properties of Cr-Al-B-N Coatings Prepared by Reactive D.C. and R.F. Co-Sputtering

The current study was undertaken to investigate the synthesis of CrAlN/BN composite coatings having super high hardness by a reactive co-sputtering using CrAl alloy and BN targets and gaseous mixture of Ar+N2, in order to eliminate the possible formation of boride bonding. CrAlN or BN phase was deposited by pulsed d.c.- and r.f.- sputtering, respectively. Plastic hardness, Hpl, and Young’s modulus, E*, of the coatings increased with BN phase ratio, reaching a maximum value of ~46 GPa and 390 GPa at ~8 vol. % of BN phase; and then decreased to ~20GPa and ~300GPa at ~18 vol.%, respectively. Only B1 structured Cr(Al)N phase was found in XRD and SAED analysis. XPS and TEM/HRTEM results revealed that the CrAlN/8vol%BN coating consists mostly of CrAlN and BN phase, which exists as an amorphous like phase among the CrAlN grains. The CrAlN/8vol%BN coating has a kind of nanocomposite structure and the super high hardness over 40 GPa is probably due to this structure.

Properties of Coating Films Synthesized from Nano Colloidal Silica and Alkoxy Silanes

Colloidal silica/silane sol solutions were prepared in variation with the ratio of silane to colloidal silica. Such sol solutions were synthesized from colloidal silica/tetramethoxysilane (TMOS)/methyltrimethoxysilane(MTMS). Sol solutions were prepared by sol-gel reaction through two step reactions. To understand their physical and chemical properties, dip coating of sol solutions was performed on the glass substrates. Contact angle and thickness of coating films increased with increasing the amount of MTMS. The surface free energy of coating films decreased with increasing amount of MTMS. Coating films were stable until 550°C. Thermal degradation temperature of coating films decreased with increasing amount of MTMS. Plastic hardness decreased with increasing amount of MTMS. Elastic portion increased with increasing amount of MTMS.

THE INFLUENCE OF AMORPHOUS PHASE TO PLASTIC HARDNESS OF SUPER- AND ULTRAHARD NANOCOMPOSITES

Hardness and yield stress of (polycrystalline) materials typically increase with decreasing grain size. However, in nanocomposites materials which consist of nanocrystalline phase (filler) embedded in amorphous phase (matrix), the hardness relation to the crystallite size curve shifts due to amorphous fraction. Experimental data show that some coatings have very different hardness ( H v > 40-105 GPa ) even though they have similar grain (nanocrystalline) size. The shifting of hardness versus crystallite size curve in nanocomposites is of particular interest. Here we use mechanical system modeling to determine the plastic hardness based on displacement of nanocrystallines during indentation process in nanocomposite nc - TiN/a - Si 3 N 4. Our hypothesis is that the nanocrystalline behave like a rigid body that move relative to each other under shear condition by indentation load. This relative movement is retarded by drag force from the surface friction between nanocrystals and amorphous phase. Our findings indicated that the influence of amorphous content in nanocomposites shift the plastic hardness as the amorphous fraction is varied. In the range of 3-13 nm grain size, one can construct several hardness versus crystallite size curve by varying the amorphous fraction. The experimental data of nanocomposite nc - TiN/a - Si 3 N 4/ a -& nc - TiSi 2 agree well with our calculation results.

Large-Scale Manufacturing of Nanoscale Multilayered Hard Coatings Deposited by Cathodic Arc/Unbalanced Magnetron Sputtering

Nanoscale multilayered (superlattice) hard coatings can be manufactured in a plastic hardness range (HP) between 25GPa and 55 GPa by a combination of cathodic arc evaporation and unbalanced magnetron sputtering (arc bond sputter technology). Using large-scale industrial physical vapor deposition (PVD) equipment and a sufficiently high pumping speed, multilayered coatings can be deposited by simultaneously operating cathodes without special shutter and shielding facilities in a common reactive-gas atmosphere. The efficiency of the process is in many cases identical to that of TiN and CrN. Temperature-resistant, wear-resistant, and corrosion-resistant coatings of various compositions have been produced under industrial conditions. So far, the main applications concentrate on metal-forming and on cutting die steel, Inconel, stainless steel, and titanium. Applications have also been found in the chemical, textile, medical, and automotive industries.

Understanding nanoindentation unloading curves

Experiments have shown that nanoindentation unloading curves obtained with Berkovich triangular pyramidal indenters are usually welldescribed by the power-law relation P = α(h − hf)m, where hf is the final depth after complete unloading and α and m are material constants. However, the power-law exponent is not fixed at an integral value, as would be the case for elastic contact by a conical indenter (m = 2) or a flat circular punch (m = 1), but varies from material to material in the range m = 1.2–1.6. A simple model is developed based on observations from finite element simulations of indentation of elastic–plastic materials by a rigid cone that provides a physical explanation for the behavior. The model, which is based on the concept of an indenter with an “effective shape” whose geometry is determined by the shape of the plastic hardness impression formed during indentation, provides a means by which the material constants in the power law relation can be related to more fundamental material properties such as the elastic modulus and hardness. Simple arguments are presented from which the effective indenter shape can be derived from the pressure distribution under the indenter.

Superhard nanocomposite coatings. From basic science toward industrialization

A variety of superhard coatings with Vickers plastic hardness exceeding 40 GPa have been reported by several research groups during the last five years (for recent reviews see refs [1,2]). However, one has to distinguish between superhard nanocomposites, such as nc-TiN/a-Si3N4, nc-TiN/a-Si3N4/a- and nc-TiSi2, nc-(Ti1-xAlx)N/a-Si3N4, nc-TiN/TiB2, nc-TiN/BN, etc. where the high hardness originates from the nanostrucutre and, therefore, remains stable upon annealing to high temperatures [1], and coatings, such as CrN/Ni, ZrN/Ni, and others [2] in which the measured high hardness is due to a high compressive stress that is induced in the coatings due to energetic ion bombardment during their deposition (e.g., by magnetron sputtering). We also summarize the recent progress in the industrial applications of the superhard nanocomposite coatings on machining tools.