Mohammed Alluaibi Chapter 4 [304406]

Chapter 4

Materials and methods

4.1. Material as received

A [anonimizat], experimental methods used for analyzing the samples have been given in this chapter. The material chosen for the current study is the titanium alloy Ti-6246 (β-transus: 940 ±5 șC) which obtained by VAR Vacuum Arc Remelting at S.C. Zirom S.A. [anonimizat]. The chemical composition of Ti-6246 alloy is shown in Table 4.1.

Table 4.1

Chemical composition in (wt. %) [anonimizat]-6246 alloy

Ten samples were included in the present study; sample I (as-received), sample II (homogenization), samples from III to VI (hot deformation in beta phase field at a temperature range 950-1100 °C) and samples from VII to X (solution heat treatment in alpha phase field with a fixed temperature) (see Fig. 4.1). The primary work was to ingot breakdown into five parts by using a precision cutter device model Metkon Micracut 200 (see Fig 4.2). The initial titanium alloy (Ti-6246) as received and after ingot breakdown processes are shown in Fig. 4.3. [anonimizat]-mechanical processes and the fifth one was kept as a spare. Table 4.2 shows the approximate dimensions (length, width and thickness) of these parts. The thickness is the most important dimension because it is mostly influenced by the mechanical process such as forging. [anonimizat] (Ti-6246) is shown in Figure 4.1.

Fig. 4.1 [anonimizat]-6246 alloy.

Fig. 4.2 Metkon MICRACUT 200.

Fig. 4.3 initial Ti alloy a) as-received, b) after ingot breakdown process.

Table 4.2

The dimensions of alloy after ingot breakdown

4.2. Homogenization treatment

The second step is the homogenization treatment above the β-transus temperature in the β-phase field. The major steps of the homogenization treatment as follows:

Operating the furnace and set the temperature at 950 șC. The furnace should be left for 1 and half hour to reach the required temperature. Fig. 4.4 depicts the furnace (The Nabertherm Furnace) that used in this work.

Putting the samples in the furnace for 6 [anonimizat] a water quench. Fig.4.5 shows the samples after being homogenized.

Fig. 4.4 The furnace used in this study (The Nabertherm Furnace).

Fig. 4.5 The samples after being homogenized.

4.3. Thermo-[anonimizat]-mechanical processes were started on the samples. Thermo-mechanical treatment processes consist of two processes: hot deformation treatment by upsetting (forging) and the final step solution heat treating. The first process includes deformation in the β phase field at different temperature ranges from 950 șC to 1100 șC. The final process contain solution heat treating in the α phase field at specified temperature 950 °C, [anonimizat] a result, led to changes in properties and microstructure of these specimens.

The major steps of the hot deformation process can be summarized as:

Operating the furnace and set the temperature at 950 șC. The furnace should be left for 1 and half hour to reach the required temperature.

Putting the samples individually in the furnace for 10 minutes with different temperature as shown in Table 4.3.

Table 4.3

Temperature and time set up for each sample

Once the samples have removed from the furnace after 10 minutes, they exposed to the forging process using hammer device to smash the samples from III to VI (the hammer weight is 117 kg with a height of 110 cm) which shown in Fig. 4.6.

Fig. 4.6 The forging device.

Then, the samples left to cooling at the ambient temperature. Figure 4.7 a shows the samples after have been forged. Moreover, the thickness of each sample has been reduced in this process (see Fig. 4.7 b). Table 4.4 present the new values of the samples thickness.

Fig. 4.7 The samples after being forged, a) top view, b) side view of the sample one.

Table 4.4

Thickness values of each sample before and after forging process

Thereafter, deformation degree of samples from III to VI have been estimated from the relation below (see Fig. 4.8)

(1)

Where,

– Is the deformation degree in, (%),

H – Is the initial thickness in, (mm),

h – Is the final thickness in, (mm).

Fig. 4.8 the relation between the temperature and the deformation degree (Estimated according to Eg.1).

The final process is solution heat treatment process of samples from VII to X at temperature 950 °C with different temperatures of hot deformation process as mentioned above, in alpha phase field it can be summarized as:

Operating the furnace and set the temperature at 950 șC. The furnace should be left for 1 and half hour to reach the required temperature.

Putting all the samples in the furnace for 10 minutes at constant temperature (950 șC).

Once the samples have removed from the furnace, they were cooling by a water quench. The temperatures and the time of hot deformation, solution heat treating processes as shown in Table 4.5.

Table 4.5

The temperatures and time of hot deformation processes, solution heat treating processes adopted for each sample

4.4. Microstructure analysis

All the samples for metallographic analysis were cut. For the samples subjected to thermo-mechanical processes, the microstructure of the specimens could be examined in order to characterize the thermo-mechanical processes and the various zones present within, looking at the microstructure of each zone and any features present. These observations were to be the basis for explaining the microstructure of the Ti-6246. The samples were prepared with a very good surface finish using a precision cutter Metkon Micracut 200 (Fig. 4.2). Subsequently, all specimens were hot mounted using a Buehler Simplimet mounting press (Phenocure black phenolic resin; Buehler, Lake Bluff, IL facility) (Fig. 4.9) within the cylindrical sampler that has dimensions from 10 to 15 mm in height (h) and 30 mm in diameter (φ) (Fig. 4.10). All samples were subjected to grinding and polishing using a Metkon DIGIPREP Accura (advanced high-end grinding and polishing system) see Fig. 4.11. The microstructure of the homogenization, hot deformation, solution heat treatment, as well as the as-received material was investigated using scanning electron microscopy (SEM) device, model (TESCAN VEGA II–XMU) as depicted in Fig. 4.12.

Fig. 4.9 Buehler Simplimet Mounting Press.

Fig. 4.10 the cylindrical specimen.

Fig. 4.11 Metkon DIGIPREP Accura device for grinding and polishing the sample.

Fig. 4.12 SEM device (TESCAN VEGA II–XMU).

4.5. Mechanical testing

The as-received material and all thermo-mechanical processes samples were mechanically investigated in tensile strength test. The tensile test was carried out using a mechanical testing machine module Deben MICROTEST-2000 – mounted inside SEM (see Fig. 4.13). The samples for the tensile test were taken from the thermo-mechanical processes (Fig. 4.7). The specimens were taken from both the hot deformation and solution heat treating processes from different direction in order to achieve a complete testing matrix. Tensile strength test samples were cut to small rectangular slides shape of approximately 2: 35 mm length, 0.6 – 0.7 mm thickness and 2 mm width. Ultimate Tensile Strength (UTS), Yield Strength (YS) and Critical Strain (εc) were estimated.

Fig. 4.13 Tensile testing apparatus (module Deben MICROTEST-2000 – mounted inside SEM).