Uwe Erb

High strength nanocrystalline cobalt with high tensile ductility

Tensile properties of fully dense nanocrystalline cobalt electrodeposits with an average grain size of 12 nm were studied at different strain rates. By decreasing the strain rate the ultimate tensile strength increased noticeably. At the lowest strain rate the elongation to failure is comparable to that of polycrystalline cobalt. � 2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

THE EFFECT OF GRAIN SIZE ON THE WEAR PROPERTIES OF ELECTRODEPOSITED NANOCRYSTALLINE NICKEL COATINGS

Department of Metallurgy and Materials Science, University of Toronto, 184 College Street,Toronto, Ontario, Canada M5S 3E4*Integran Technologies Inc., 1 Meridian Road, Toronto, Ontario, Canada M9W 4Z6(Received August 25, 2000)(Accepted September 13, 2000)Keywords: Nanocrystalline nickel; Wear; Electroplating; Grain boundariesIntroductionNanocrystalline materials, as a result of the considerable reduction of grain size and their significantvolume fraction of grain boundaries and triple junctions, have exhibited many unusual mechanical,physical, chemical and electrochemical properties compared with conventional polycrystalline oramorphous materials [e.g. 1,2]. For many engineering applications, wear resistance is one of the mostimportant mechanical properties because wear accounts for more than 50% loss of all materials inservice [3]. Grain size reduction has been previously shown to lead to significant improvements of thewear resistance in nanocrystalline materials. For the case of nanostructured WC-Co composites, forexample, the reduction of WC grain size to 70 nm nearly doubled the abrasive wear resistance overconventional cermets [4]. Nanocrystalline nickel with 10 ; 20 nm grain size made by electrodepositionshowed 100 ; 170 times higher wear resistance and 45 ; 50% lower friction coefficient thanpolycrystalline nickel with 10 ; 100 mm grain size in the pin-on-disk test [5]. When the grain size ofaluminum was reduced from 1 mm to 16 nm, the peak coefficient of friction decreased by 57% in theminiature pin-on-disk test [6].In this study, the effect of grain size reduction on the wear resistance of electrodeposited nanoc-rystalline pure nickel coatings was investigated quantitatively by the Taber abrasive wear test, astandard test often applied in industrial testing.ExperimentalThe substrates for nanocrystalline nickel coatings were AISI 1010 mild steel with a size of 10 3 10 cm

Mechanical properties of nickel silicon carbide nanocomposites

Abstract Nanocomposite materials consisting of a nanocrystalline Ni matrix (grain size 10–15 nm) reinforced with sub-micron size SiC particulates (average particle size: 0.4 μm) up to 10.5 vol.% have been produced by pulse electrodeposition. Substantial improvements in mechanical properties including hardness, yield and tensile stress were obtained for the nanocomposite material, as compared with conventional Ni–SiC composites with a matrix grain size in the micrometer range. Tensile strengths up to four times that for conventional polycrystalline Ni and two times that for conventional polycrystalline Ni–SiC of comparable SiC content was measured. The tensile and yield strengths of the nanocomposite material with SiC content less than 2 vol.% were higher than those for pure nanocrystalline Ni of comparable grain size. For these nanocomposites an unexpected increase in tensile ductility was also observed when compared to pure nanocrystalline nickel. At higher SiC content (>2 vol.%) the strength and ductility were found to decrease to the detriment of the nanocomposite. Particle clustering was considered the main cause of this decrease.

The relationship between hardness and abrasive wear resistance of electrodeposited nanocrystalline Ni–P coatings

Abstract The effects of alloying with phosphorus and subsequent heat treatment on the relationship between hardness and abrasive wear resistance of electrodeposited nanocrystalline Ni–P coatings were studied using Taber wear testing. For both the as-plated and heat-treated nanocrystalline Ni–P coatings, strong linear relationships between hardness and Taber wear resistance were observed.

The effects of triple junctions and grain boundaries on hardness and Young's modulus in nanostructured Ni-P

Abstract Hardness and Young’s modulus were measured on a series of nanocrystalline Ni–P samples. With decreasing grain size, a transition from regular to inverse Hall–Petch relationship and a reduction in Young’s modulus at the smallest grain sizes was observed, which can be attributed to grain boundary and triple junction effect.

An initial analysis of mechanisms leading to late stage abnormal grain growth in nanocrystalline Ni

Abstract A late stage of abnormal grain growth, having unusual planar abnormal growth interfaces, is observed during the isothermal annealing of electrodeposited nanocrystalline Ni and Ni–Fe alloys. This communication presents observations of grain embedding and the presence of a wetting, sulfur-rich second phase at the abnormal growth interface and suggests a growth mechanism.

A comparison of the corrosion behaviour of polycrystalline and nanocrystalline cobalt

The corrosion behaviour of polycrystalline (grain size: 8 μm) and nanocrystalline (grain size: 12 nm) Co was studied in 0.25 M Na2SO4 solution. It is shown that grain size reduction has little effect on the overall corrosion performance of Co. The role of S impurities in nanocrystalline Co is also discussed.

THE EVOLUTION OF TEXTURE AND GRAIN SIZE DURING ANNEALING OF NANOCRYSTALLINE Ni-45% Fe ELECTRODEPOSITS

The study of thermal stability of nanocrystalline materials is of great importance for the general assessment of potential technological applications. This is especially true for nanocrystals obtained by electrodeposition. A high electrode polarization, usually used during electrodeposition to reduce grain size, produces materials that are not in a state of equilibrium. This results in a large driving force for grain growth at elevated temperatures. The purpose of this investigation is to examine the thermal stability of nanocrystalline Ni-45 wt.% Fe alloy produced by electrodeposition. Of particular interest is the evolution of texture during annealing and the change of hardness.

Microstructure and texture development of copper single crystals deformed by equal-channel angular pressing

The microstructures of copper single crystals after one equal-channel angular pass have been examined in order to clarify the mechanism of deformation in simple shear from a crystallographic aspect. The deformed microstructures were strongly influenced by the initial orientation and can be categorized into three distinct groups, namely heterogeneous structure with shear bands and mechanical twins (group I), deformation bands (group II) and homogeneous structure as a result of uniform crystal slip (group III).

A low-cost method to produce superhydrophobic polymer surfaces

Here, we introduce a novel and inexpensive template-based structuring process to create superhydrophobic polymer surfaces adapted from the naturally occurring micro/nano structured surfaces found on the superhydrophobic leaves of the quaking aspen tree. Electroformed nanocrystalline nickel coupons were sandblasted and chemically etched to create a negative reproduction of the aspen leaf surface structure. These nanocrystalline nickel samples were then employed as re-useable templates and pressed against various polymers at elevated temperatures, transferring the desired superhydrophobic structure to their surfaces. This structuring process resulted in water contact angles above 150° and tilt angles below 5° for polyethylene, polypropylene and polytetrafluoroethylene samples. In addition, the effects of temperature, water drop size and surfactant concentration on these pressed polymer surfaces were investigated to assess potential application limitations for these surfaces.