Gino Palumbo

Influence of grain boundary character distribution on sensitization and intergranular corrosion of alloy 600

The objective of this study was to assess, for the first time, the potential impact of ``Grain Boundary Design and Control`` on the bulk sensitization and intergranular corrosion resistance of a commercial corrosion resistant nickel-based austenitic alloy: Alloy 600 (UNS N06600). Increasing the special grain boundary ({Sigma} {le} 29) frequency in thermomechanically processed Alloy 600 from 37% to 71% has been shown to result in commensurate decreases in bulk intergranular corrosion susceptibility in both the solution annealed and sensitized condition; these findings being attributed to both the intrinsic corrosion resistance, and resistance to solute segregation and precipitation exhibited by structurally-ordered low {Sigma} grain boundaries. These results provide considerable promise for the practical application of grain boundary design and control considerations in the general field of corrosion prevention and control.

Deviations from hall-petch behaviour in as-prepared nanocrystalline nickel

2,106,004 1/1938 Inglee .................................. 204/300 R 2,764,540 9/1956 Farin et al. .......................... 204/1297 3,103,235 9/1963 Stringham ................................. 138/97 3,125,464 3/1964 Harmes ................................... 18/105 3,287,248 11/1966 Braithwaite ............................. 204/260 3,618,639 11/1971 Daley et al. ............................ 137/28 3,673,073 6/1972 Tobey et al. ............................ 204/226 3,804,725 4/1974 Haynes .................................... 205/104 4,080,268 3/1978 Suzuki et al. ........................... 205/131 4,120,994 10/1978 Inoue ...................................... 427/239 4,200,674 4/1980 Inoue ...................................... 427/290 4,227,986 10/1980 Loqvist et al. .......................... 204/209 4,280,882 7/1981 Hovey ....................................... 205/50

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.

Electrodeposition of nanocrystalline Ni-Fe alloys

Abstract Thick nanocrystalline Ni and Ni-Fe alloy deposits with grain sizes less than 30 nm and containing iron up to 28 wt.% were produced by electrodeposition at rates in excess of 100 μm per hour. It is shown that the grain size, macrotexture and microtexture of these materials is strongly dependent on the amount of iron co-deposited with nickel. With decreasing grain size, the hardness of the materials initially increases following the regular Hall-Petch relationship. However, starting at grain sizes of approximately 18 nm, a deviation from the regular Hall-Petch behavior is observed leading to softening at the smallest grain sizes.

On the creep behaviour of grain boundary engineered nickel 1

Abstract Grain boundaries described by low-Σ CSL relationships (i.e. Σ ≤ 29) have previously been shown to be resistant to grain boundary sliding, cavitation and fracture. The present work reports on efforts to reduce creep rates in conventional polycrystalline nickel by increasing the frequency with which these ‘special’ interfaces occur in the microstructure. Suitable thermomechanical processing was employed to enhance the frequency of ‘special’ grain boundaries (Σ ≤ 29) in 99.99% Ni from 13 to 66%, resulting mostly from the formation of twins (23) and crystallographically-related 29 and 227 boundaries. This 53% increase in the fraction of low-2 boundaries produced reductions of 16-fold in the steady-state creep rate and six-fold in the primary creep strain. Microstructures having ‘special’ boundary frequencies of less than 50% exhibited significant cavitation almost exclusively along ‘random’ boundaries (i.e. Σ > 29) at or near triple points. No gross cavitation was evident in microstructures containing ‘special’ boundary fractions of 66%. Such improvements in creep properties provide considerable promise for the application of a ‘grain boundary engineering’ approach to developing interfacial materials for structural applications.

Synthesis, structure and properties of electroplated nanocrystalline materials

Abstract Electroplating is an economically viable production route to synthesize porosity-free pure metals, alloys and composite materials both as coatings and in bulk form. Some properties of electroplated nanocrystals differ from those observed on nanostructured materials prepared by other techniques; these differences may be attributed to residual porosity. Triple junctions have been shown to strongly effect certain properties of nanostructured materials and should not be overlooked in future interpretation of properties of both nanocrystalline and conventional polycrystalline materials.

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.