Showing papers in "Journal of Materials Science Letters in 1983"

The lattice thermal expansion of hydroxyapatite

Abstract: La dilatation thermique le long des axes α et c du Ca 10 (PO 4 ) 6 (OH) 2 est determinee, entre 22 et 1000°C a l'aide de la diffraction RX a haute temperature

The micromorphology of an injection moulded thermotropic liquid crystal polymer

Abstract: Micromorphologie d'un copolyester d'acide paracetoxybenzoique et d'acide acetoxynaphtalique par diffraction RX et microscopie electronique a balayage

Ductility of the superplastic Pb-Sn eutectic at room temperature

Abstract: In the classic experiments of Pearson [1], conducted on the Bi -Sn and P b S n eutectic alloys in 1934, very high tensile elongations were obtained when test samples were pulled to failure under conditions of approximately constant stress. Fc, r example, the Bi -Sn alloy exhibited an elongation to failure of 1950% and the P b S n alloy pulled out to an elongation of 1505 %. It is surprising to note that, in general, very high elongations have not been attained in any of the many subsequent tests conducted on various superplastic alloys at room temperature. Tabulations of much of the available data are given in several reviews [2 -6 ] , and the maximum elongations reported at room temperature are usually < 1000% and invariably of the order of 213,0 to 500 %. Examples of these low elongations are provided by tests on the B i In eutectic [7], a Pb -Cd alloy [8], various Pb-T1 alloys [9], S n t wt% Bi [10], various dilute Zn-A1 alloys [11 -16 ] and the Z n 2 2 w t % A1 eutectoid [17]. In the P b 6 2 w t % Sn eutectic, the maximum elongations at room temperature are usually < 1000 % [ 18-21 ], although Avery and Backofen [22] used various heat treatments and were able to achieve a maximum elongation o f 1584%. It seems likely that the difficulty experienced in the more recent experiments in attaining very high elongations in the P b S n eutectic at room temperature is due to the use of commercial tensile testing machines operating at fairly fast strain rates. Inspection o f the early data indicates that the creep tests of Pearson [1 ] were conducted at a nominal strain rate of the order of 10 -6 sec -1 whereas the more recent tensile tests on the P b S n eutectic have been restricted to strain rates faster than about 10 ---4 sec -1 . T h u s , the present investigation was undertakel~ to examine this dichotomy in more detail by measuring the ductility of the P b S n eutectic alloy at room temperature over a range of strain rates down to < 10 -s sec -1. The P b 6 2 wt % Sn alloy was prepared from 99.999 % purity lead and 99.995 % purity tin by melting in air in a graphite crucible, chill-casting into an ingot having a thickness of 1.0 cm, and then rolling at room temperature to a final thickness of 0 .254cm. A spectrograp~c analysis revealed the following impurities in ppm: Ag 0.2, A1 0.5, Au 1, Bi 0.7, Ca 0.1, Cd 0.1, Cu2, Fe 1, In 1, Mg 0.2, Mn 0.1, Si 0.3 and T1 0.5. Tensile spedmens, having a gauge length of 1.27 cm and a gauge width of 0.64 cm, were cut from the sheet parallel to the rolling direction. Each specimen was annealed in air for 1 h, at 433 K to give an average spatial grain size, d (= 1.74 x mean linear intercept), of 6.1/~m. The specimens were tested at room temperature (298 + 2K) by pulling to fracture in an Instron machine operating at a constant rate of cross-head displacement; the tests were conducted at equivalent initial strain rates, ~, in the range from 6.6 x 10 -2 to 6.6 x 10 -6 sec -1. It should be noted that earlier work at a temperature of 413K, using the same alloy with a grain size of 6.9/~m, gave elongations o f up to > 4800% with an initial strain rate of about 10 -4 sec -1 [23]. Fig. 1 shows the calculated curves of the true stress, o, against true strain, e, for five selected initial strain rates each differeing by one order of magnitude. Each test was continued to fracture, and Fig. 2 shows the results plotted as AL/Lo(%) against the initial strain rate, ~, where AL is the total increase in length at the point of failure and Lo is the initial gauge length. These data show that the elongations are less than about 500% at initial strain rates above about 10 -4 sec ~1 in accordance with earlier reports [19-21 ], but there is a marked increase in the fracture elongations at strain rates below about 10 -4

Rapid heating of Fe-Si-B metallic glasses

Abstract: Etude de la transformation amorphisation-cristallisation mutant les vitesses de chauffage et refroidissement des alliages amorphes Fe 75 Si 15 B 10 et Fe 75 Si 12 B 13 . Les alliages chauffes et refroidis restent a l'etat amorphe tandis que les alliages refroidis lentement recristallisent soit au chauffage, soit au refroidissement

Effect of hydrogen attack on the strength of high purity copper

Abstract: Experimental as well as theoretical studies [1-4] in relation to the influence of heat treatment on the structural and mechanical behaviour of metals and alloys in hydrogen atmosphere have been extensively undertaken in recent years. Pishko et al. [1] observed that the ultimate tensile strength of various steels pulled at 77 K was a fmaction of the time of exposure to hydrogen at 723 K, due to the formation of voids on certain grain boundaries. Feltham and Evans [2] found that creep in 5N pure copper single crystals between 773 and 1143 K was also significantly influenced by hydrogen uptake. More recently Butt and Feltham [3] studied the effect of hydrogen on grain growth in 5N pure copper at 1073 K; the grain size was found to decrease rather than increase, with increasing time of isothermal annealing, due to the diffusion of hydrogen to grain boundaries. On the theoretical side, Hirth [411 made an attempt to account for the observations on the basis of the distribution of vacancy chemical potential near a nucleating and growing void when cavitation occurs in either creep [5] or hydrogen attack [1-3] of metallic crystals. The main object of the present work was to investigate the effect of hydrogen uptake on the yield strength of 5N pure copper in the range 77 to 300 K. The polycrystalline copper of 5N purity used was supplied by Metals Research Limited, Royston, England in the form of cylindrical rods of 1 cm diameter. Specimens, 2cm long, were cut from the "as-received" rods by means of a fine saw. They were grouped into four batches, and each batch was sealed into a separate silica tube filled with hydrogen at 100 tore They were then annealed for 120 rain at 523 K to minimize internal stresses, before the subsequent isothermal grain growth extending over periods of 15 to 120 rain at 1073 K. Mean grain diameters, 0.9 and 0.35 mm in Fig. 1 and 0.60, 0.45, 0.35 and 0.33 mm in Fig. 2 were obtained by the line-intercept method. Chemical polishing of some of the sp~.'cimens of different grain sizes for about 4rain at 323 to 528K in a solution containing 25vo1% H3PO4, 25vo1% acetic acid and 50vo1% concentrated nitric acid revealed numerous "craters" on the

Internal stresses in austenitic steels cathodically charged with hydrogen

Abstract: Hydrogen cathodic charging of austenitic stainless steels has been manifested by a reduction of the ductility under dynamic tensile stresses and by the appearance of nonductile fracture surfaces. The electrolytic charging process provides a huge hydrogen fugacity, and thus large amounts of hydrogen may be driven into the specimen. This process leads to the development of internal stresses, phase transition to a ' and e martensite, and intensive intergranular and transgranular cracking [1-6]. The purpose of this study is to find the reasons for the development of internal stresses as a result of cathodic charging of stainless steel and to correlate between the surface cracking and internal stresses. The studies were carried out on a type 316 austenitic stainless steel. The samples were obtained in the form of 0.1 mm thick sheets and were solution annealed. The grain size, as measured by ASTM E-112 method, was of the 10.5 number ASTM, corresponding to the mean grain size of 9.4 ~tm. The samples were cathodically charged for 24 h at room temperature in an 1 N H2SO4 solution with 0.25 g per litre of NaAsO2 added as a hydrogen recombination poison. A platinum counterelectrode and a current density of 50mAcm -: were used. A conventional Philips diffractometer equipped with step-motor, programmer, and teletype printer was used for the X-ray diffraction study. The choice of the X-ray wavelength is of special importance. In diffraction with reflection (BraggBrentano) geometry, we actually obtain information only from the thin surface layer of the flat sample. The intensity I t of rays scattered by the surface layer of thickness t is equal to [7]: