[en] This work aims to characterize the 36 NiCrMo 6 steel in monotic traction. The tested samples were subjected to mechanical surface treatment (MST) by diamond ball burnishing. This process allow it possible to modify the physical and geometrical properties of the material. The stress-strain diagram obtained were processed and digitalised. The hardening domain was modelled and rational curves were established, taking into account the stresses triaxiality. Thus, the work hardening exponent of material considered was evaluated. The effect of ball burnishing on this exponent has studied in proceeding a comparative manner between burnished and machined surface. The results obtained show that by applying the optimal parameters for burnishing, the work hardening exponent of pre-machined surface layer can be increased by 10%, where n_B = 0.407 (n_T = 0.312 machined surface). (paper)

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[en] This paper reviews the work hardening, recovery and recrystallization mechanisms in alloys containing dispersed precipitates. In the section on work hardening, the influence od spacing, particle size and shape on the density and distribution of dislocations have been discussed. They represent a large part of the energy stored in the material following drformation, which in turn is driving force for recrystallization. Next, the role of precipitates on recovery, on the formation and the growth of recrystallized regions has been discussed in detail. The competition between recovery and recrystallization and recrystallization of supersaturated solid solutions have also been mentioned. Finally, the technological relevance of the aspects treated in this paper has been discussed. (author)

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[en] Presented are results of investigation on the effect of roughness parameters on durability of samples made of the VT6 titanium alloy in the conditions of pure bending and repeated tension and on hardening efficiency by the methods of shot-shock, pnevmodynamic and vibrodynamic treatment. It is shown that VT6 alloy is less sensitive to roughness of surface under studied conditions of repeated loading than high-tensile steels, and efficiency of hardening treatment depends both on the hardening method and on the initial value of roughness. There exists an optimum range of surface roughness at which the highest increase of durability is being provided in the result of application of definite methods of surface hardening

[en] This thesis investigates the mechanisms by which ion implantation can affect those surface mechanical properties of ceramics relevant to their tribological behaviour, specifically hardness and indentation fracture. A range of model materials (including single crystal Si, SiC, A1₂0₃, Mg0 and soda-lime-silica glass) have been implanted with a variety of ion species and at a range of ion energies. Significant changes have been found in both low-load microhardness and indentation fracture behaviour. The changes in hardness have been correlated with the evolution of an increasingly damaged and eventually amorphous thin surface layer together with the operation of radiation-, solid-solution- and precipitation-hardening mechanisms. Compressive surface stresses have been shown to be responsible for the observed changes in identation fracture behaviour. In addition, the levels of surface stress present have been correlated with the structure of the surface layer and a simple quantitative model proposed to explain the observed stress-relief upon amorphisation. Finally, the effects of ion implantation upon a range of polycrystalline ceramic materials has been investigated and the observed properties modifications compared and contrasted to those found for the model single crystal materials. (author)

[en] This thesis deals with several aspects of copper precipitation and irradiation hardening in Fe-Cu alloys. i) The stability of copper precipitates in a ferritic matrix has been investigated using HREM to determine the size at which the b.c.c.→9R transformation occurs in thermally aged Fe1.3wt%Cu alloys. This size has been shown experimentally to be ∼12nm during ageing at 550 deg. C. Precipitates of size 4-12nm transform during cooling to room temperature or below. ii) Immediately after the b.c.c.→9R transformation the angle, α, between fringes in adjacent twin bands is approximately 129 deg. Plane rotations and untwinning can be induced in thermally-aged specimens by in-situ electron irradiation with 400keV electrons. After some time under the beam the planes appear to have rotated, reducing a to about 122 deg. Under electron irradiation two mechanisms were observed: i) rotation of the (009)_9R planes without the precipitate first untwinning, ii) untwinning where one 9R twin variant grows at the expense of the other, confirming directly the untwinning mechanism proposed previously. Plane rotation and detwinning occurred simultaneously. iii) Ion irradiation of an Fe-1.3wt%Cu alloy was carried out at the Hahn-Meitner Institute in Berlin, using 300keV Fe⁺ ions at temperatures between 20 deg. C - 550 deg. C at displacement rates of 10^-3-10^-2 dpa(s)^-1 for doses within the range 1-30dpa. Copper precipitates were found to keep their shape but decrease in size under all irradiation conditions. The mechanism of dissolution is described as a balance between the dissolution of precipitate by cascades and the reprecipitation of the copper due to the movement of copper at the irradiation temperature. iv) High-resolution microscopy of an Fe-1.3m%Cu alloy neutron irradiated to doses of 0.008dpa and 0.06dpa at ∼280 deg. C revealed small copper precipitates having α ∼ 122 deg. - 126 deg. It was deduced that many of these precipitates had transformed from b.c.c.→9R in the reactor at ∼280 deg. C. Precipitate sizes did not depend significantly on dose, with a mean diameter of ∼3.4±0.7nm and ∼3.0±0.7nm for the 0.008dpa and 0.06dpa material respectively. The number densities of transformed precipitates were ∼1.8x10²¹m^-3 and ∼8.5x10^2m-3 respectively. GIF-EELS chemical mapping analysis gave total number densities of 5.6x10²²m^-3 and 6.0x10²²m^-3 respectively. v) Finally, weak-beam electron microscopy was used to investigate neutron irradiated 'pure' iron 'Hawthorne' 1A and 2A alloys irradiated to a dose of 0.06dpa at ∼280 deg. C. The dislocation loops in the 1A alloy had a mean size of ∼2.8±0.1nm, while those in the 2A alloy had a size of ∼3.4±0.1nm. About 80% had Burgers vector b=a<100> and the remainder were of type b=a/2<111>. The precipitate number densities for the 1A and 2A alloy were ∼8.5±0.9x10²¹m^-3 and ∼6.6±0.7x10²¹m^-3 respectively. The visible defect populations account for a maximum of 59% and 75% of the measured hardening values for the 1A and 2A alloys respectively. The loops are stable under thermal annealing to about 430 deg. C, which suggests they have an interstitial nature. No voids were observed. (author)

[en] The alloys studied are derived from Inconel 718 by increasing the ratio R=(Ti+Al)/Nb, which favor precipitation of the γ'-Ni₃(Ti,Al) phase during aging at the expense of the metastable γ''-Ni₃Nb phase responsible for considerable hardening of the reference alloy. It was possible in this way to define a region of the composition space R and S (S=Ti+Al+Nb) such that any alloy of this region gives rise to an original precipitation where the particles consist of γ' phase cubes plated on all six faces with the γ'' phase. These compact morphology precipitates show great stability of nature, size and shape at steady temperatures up to around 700 deg C, unlike Inconel 718 where the growth of the γ'' plates and their subsequent conversion to the stable β-Ni₃Nb phase cause the alloy to age rapidly above 600 deg C. A comparison of the mechanical properties of Inconel 718 and one of the compact morphology precipitation alloys shows that for the derived alloy these properties can be as good or better after the aging treatment (hardness, tensile strength, short-term creep, low-cycle fatigue) and distinctly improved after long maintenance at temperatures of 700 deg C or above (hardness, long-term creep)

[en] The importance of aluminium sheet forming in aero spatial industry makes it necessary to study those parameters that control the behaviour of material during the process. Tensile properties, strain hardening exponent n and strain rate sensitivity m in 7075 aluminium alloys have been studied to relate forming behaviour with control parameters. Tests on O, W, and T6 tempers have been performed, to determine the influence of heat treating. Finally, both longitudinal and long transverse directions tensile specimens have been obtained to analyze the anisotropy. (Author) 9 refs