Transient creep characteristics of Tin Base Alloy
Citation: Transient creep characteristics of Tin Base Alloy, American Research Journal of Physics, vol 4, no. 1, 2018, pp. 1-12
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Transient creep experiments were inspected under several used stresses extended from 10 to 19.5 MPa for three ternary eutectic (Sn-3.5Ag- xIn) alloys, where x takes the values (x= 0.5, 1 and 1.5 In ). All tests at temperatures, ranging from 303 to 393 K. The transient creep is classified by εtr = βtn, Where εtr and t are the transient creep strain and time. The exponent n was found to have values extended from 0.646 to 1.59 for Sn-3.5Ag-0.5In, ranging from 0.82 to 1.64 for the second alloy Sn-3.5Ag-1In, and finally it ranging from 0.94 to 1.74 for Sn-3.5Ag-1.5In. The value of β was found to have values ranging between -14.38 to -7.2, -13.85 to -7, and -13.55 to -6.8 for the three alloys; the activation enthalpy shows that the operating mechanism controlling the tin process may be the grain bounding diffusion. Also, X-ray diffraction examination display the permanence of both β-Sn rich phase and the intermetallic compound Ag3Sn and very little particles or residue from the intermetallic composition γ-In Sn4.
Keywords: Binary alloy; intermetallic composition; transient creep; ternary alloys.
The transient creep distortion is specified by the motion of mobile dislocations and finish in their effective locking at obstacles or is originally believed as dislocation consuming source(1). Tin-indium alloys are of individual importance, because the existence of indium appears to confer the special properties of wetting and bounding (2) to glass or glazed surfaces, and gives an increase of the low hardness and the resultant low mechanical strength of Sn (3). These alloys called Pewters (alloys of more than 90% Sn) are utilized especially as solders for packing and interconnection in the electrical, electronic, owing to their ease of fabrication into any needed form. Also, these alloys are used for utensils; they have been investigated (4,5). Few publications (not many) dates in literature in the mechanical properties of Sn-In alloys, and Sn-Ag-In alloys have been done.
The aim of the present work is destined to give some information about mechanical and structure properties of the present alloy Sn-Ag-X In.
The Sn-3.5Ag-0.5In, Sn-3.5Ag -1.0In, and Sn-3.5Ag -1.5In alloys or (Sn-Ag-xIn) where (x= 0.5, 1.0, and 1.5) were prepared from Sn (purity 99.99%) and Ag (purity 99.99%) and high purity Indium (4N or 99.99%). The ingots were rolled to wires (radius 0.4 mm), and 5 cm gauge length. In this study the wires of Sn- Ag-In alloys were annealed at 453K for 2h to eliminate the cold work introduced during swaging and then slowly cooled to room temperature at a steady cooling rate Tˈ=2x10-3 K/sec. After this heat treatment for all samples; they were considered to be completely precipitated (6). Creep deformations were completed on annealed wire samples. The softly cooled samples were crept under fixed applied stresses (from 10 MPa up to 19.5 MPa). These tests were achieved in an amended model of creep machine provided with computer. The accuracy of temperature measurement is of the order of ±1K. Strain measurement were do with an accuracy of ±1x10-5. Energy-dispersive X-ray spectroscopy (EDS) analysis is used for chemical characterization of the used sample; the acquired results from EDS analysis are corresponding to tested alloys as shown in Table 1 and Fig.3. A solution of 2% HCl, 3% HNO3 and 95% (vol.%) ethyl alcohol was prepared and used to etch the samples. Phase identification of the used samples accomplished out by X-ray diffractometry (XRD) at 40 KV and 20 mA using Cu Kα radiation with diffraction angles (2θ) from 20.99o to 99.99o and a fixed scanning speed of 1o /min.
RESULTS AND DISCUSSION
The test of the X-ray diffraction model has been given in Fig.1; it displayed that Sn-3.5Ag-0.5In, Sn-Ag1.0In, and Sn-3.5Ag-1.5In alloys shows only two phase structure, that is, β-Sn rich phase. In addendum to the intermetallic compounds as Ag3Sn is the other phase. The transient strain is given by the equation (1) (7):
εtr = βtn (1)
where εtr and t are the transient creep strain, and time, β and n are constants relying on the empirical experience states.
It can be observed in Fig.2a that the microstructure of the Sn-3.5Ag binary alloy consists of relatively fine Ag3 Sn precipitates in the white β-Sn matrix In Fig.2b, the microstructure of the Sn-3.5Ag-0.5In alloy showed a coarse γ-InSn4 in the β-Sn matrix. Fig.2c represented the microstructure of Sn-3.5Ag-1.0In alloy, where the volume fraction of γ-InSn4 is increased, in addition to, fine Ag3 Sn, and β-Sn matrix. Fig.3a; represented SEM images of the Sn-3.5Ag alloys,m the microstructure possessed β-Sn areas, fine Ag3 Sn precipitates, and eutectic area. In Fig.3-b EDS analysis of the Sn-3.5Ag alloys.
Creep curves of Sn-3.5Ag -In alloys
Fig.4a-e displays typical creep curves of the three tested solder alloys expressed as creep rate versus time at constant test temperature in the rang from 303 to 393K in 20K growing under applied stress level in the range of 10.5 to 19.5 MPa for all tested materials. Typical examples of creep curves of alloys are presented in this Fig.