1.1 Background
Plasma nitriding is one of the surface hardness processes whereby a surface of a material is shot by plasma. Since plasma nitriding is a process, it requires a machine to be able to execute this process. Therefore, introducing the plasma focus device as also known as plasma gun. The plasma focus device (plasma gun) is discovered and developed early in the 1960s by two physicists, J.W.Mather and N.V. Filippov. The device operates using a high electric current which leads to electromagnetic acceleration and compression. The gases inside the chamber reacts to the high current which produces heat and then compress the gases to high temperature and densities. The compression of the electromagnetic of a plasma is labelled as a “pinch”. Which this pinch is a particular discharge where high voltage is executed on a low pressure gas between coaxial cylindrical electrodes. There are a few electrodes which are placed few inches across each other. These electrodes are enclosed in a vacuum chamber whereby low pressure gas is filled in the spaces between them. The pulse of electricity of the capacitor bank and energy storage device is discharged across the electrodes. The current flows from the outer electrode to the inner electrode to the gas. Whereby the gases are compressed into a pinch focus where nuclear fusion (focus fusion) happens.
Figure 1: Scheme Circuit and Plasma Dynamics
(Source: Braz.J., 2004)
Where discharge starts from I then to II, III where the electromagnetic acceleration begins and IV where the pinch is formed.
The usage of the plasma focus device which includes modification and fabrication of materials, x-rays and etc.. In this project, modification of materials falls on the scope of this project. The plasma focus device used in the lab is similar to the Mather Model device as shown below.
Figure 2: Plasma Focus Device, Mather Model
1.1 Plasma
Plasma is another state of matter whereby it cannot be classified or grouped with the three states of matter which are solid, liquid and gas. Plasma is a very unique state of matter which it consists of protons, neutrons and electrons, whereby the electrons are free electrons. These electrons removed from their individual atoms. Therefore, creating free electrons and positive ions. Plasma are gasses that undergoes very strong high heat where it becomes a new state of matter. Since free electrons are present, it allows them to conduct electricity. This proves the difference between gas and plasma, that gas are not able to conduct electricity but plasma are able to conduct electricity.
1.2 Aim
There are many ways to modify/improve the hardness of a material. In this project, the usage of plasma nitriding is used to modify the hardness properties of the material. The material chosen for this project is AISI 304 alloy steel (Stainless Steel). The surface hardness of the steel is to be observed and tested to examine the changes in hardness properties.
1.3 Objectives
- To determine the effect of surface hardness of AISI 304 stainless steel when nitrided with ten ion beam shots in a plasma focus device
- To determine the relationship between the surface hardness of AISI 304 stainless steel before and after 10 ion beam shots of plasma nitriding
1.4 Scope of Research
This project is conducted to determine the effect of the surface hardness of AISI 304 stainless steel when nitrided with ten ion beam shots in a plasma focus device. A total of ten pieces of samples (AISI 304 Stainless Steel) are experimented each to achieve an average result.
In addition, to determine the relationship between the surface hardness of AISI 304 stainless steel before and after ten ion beam shots of plasma nitriding, Vickers Hardness test is used to test the surface hardness. The test is conducted multiple times on the ten pieces of samples, before plasma nitriding, annealing, and after plasma nitriding. The data is then analysed and tabulated and plotted in a line graph.
1.5 Report Organization
Chapter 1 contains the brief explanation of the history, plasma, mechanics of the plasma nitriding process and plasma focus device. With addition of the aims and the objectives of the project.
Chapter 2 contains the literature review. This contains various important information and detailed explanation of the materials, devices used and processes. Which includes detailed explanation of AISI 304 stainless steel, plasma focus devices, annealing, milling and polishing processes. The journals, research articles are mentioned in this chapter for better understanding.
Chapter 3 contains the methodology. Which explains the experimental procedure of the material to be prepared for plasma nitriding process. Brief explanation of the material and mechanical properties of AISI 304 stainless steel, geometry and dimensions, milling and polishing process.
Chapter 4 contains the results. This part contains the expected outcome of the effect of chamber pressure on the surface hardness of AISI 304 stainless steel when nitrided with ion beam shots based on the research done.
Chapter 5 contains the conclusion and the recommendations for further work. This includes the future works of stage 2 of the project which would play a huge part.
CHAPTER 2
LITERATURE REVIEW
2.1 AISI 304 Stainless Steel
AISI 304 stainless steel is considered as one of the most commonly used stainless steel. This stainless steel is considered as of the austenitic steels due to its composition of 18% of chromium and 8% nickel. Austenitic steels have a wide range of applications which one of it includes industrial technologies. This is due to their good weldability, good corrosion resistance, good malleability and etc.. By having these composition, the steel converts from ferrite to austenite. AISI 304 stainless steel contains various of alloying elements which are carbon, manganese, chromium, nickel, silicon, nitrogen, phosphorus and sulphur. These alloying elements each have a different impact on the material. The amount of composition varies on different grade of stainless steel. For AISI 304 stainless steel, the list of composition is listed below;
• Carbon: Maximum of 0.07%
• Manganese: Maximum of 2%
• Chromium: Between 17.5%-19.5%
• Nickel: Between 8.0%-10.5%
• Silicon: Maximum of 1%
• Nitrogen: Maximum of 0.11%
• Phosphorus: Maximum of 0.045%
• Sulphur: Maximum of 0.03%
The carbon compound is added into iron to make steel. The purpose of it is to increase hardness and the strength of the iron. Whereby manganese is added to increase strength, hardenability, toughness and improving the hot working process. The existence of nickel in the stainless steels makes the steel more ductile and also enhance the corrosion resistance and also to transform all the ferrite to austenite. The purpose of converting it to austenite is to make sure it is a single phase. Whereby to decrease any errors when conducting the experiment, all the samples are to be converted to a single phase which is austenite. The higher the ratio of chromium compound in the steel, the tougher the corrosive resistance of the steel.
In order to increase its hardness and strength, AISI 304 stainless steels are to be cold worked to improve it, since they cannot be heat treated. In addition due to the presence of nickel compound in the steel, which modifies them to become non-magnetic.
The figure below shows the mechanical properties of AISI 304 stainless steel;
Figure 3: Mechanical Properties of AISI 304 Stainless Steel
(source: ASM Aerospace Specification Metals Inc)
2.2 Annealing
Figure 4: Annealing Process
(Source: Instructables)
Annealing is a heat treatment process which changes the properties of the steel. It is commonly used to increase the ductility of the material hence at the same time reduce the hardness of the material. Whereby in this case to increase the machinability of the material to prepare it go through machining and plasma nitriding process. In order to maintain precision and accuracy of the result, the annealing process done on the stainless steel have been set to a single phase which is austenite. Using the two phase diagram in the figures below;
Figure 5: Phase Diagram
(Source: Fig.9.24, Callister & Rethwisch 8e.)
Figure 6: Phase Diagram 1
(Source: )
Based on the AISI 304 stainless steel material properties chart, the carbon content has a maximum composition of 0.07%. Hence taking 0.07% of carbon, austenite forms when the material reached a temperature approximately of 950°C. This proves that in between 950°C and approximately 1230°C, the material is at the austenite phase. Whereby the austenite phase is in a single phase. Above 1230°C and approximately 1420°C, the material goes into a phase where there is a mixture, mixture of both ferrite and austenite. Single phase is recommended where it is easier to control and to improve the accuracy of the results. Every material has its melting point, where for AISI 304 stainless steel, the melting point is at roughly 1400°C to 1455°C. The point where it reaches its melting point the stainless steel turns partially into liquid form. Austenite phase is also called the critical point, whereby the formation of austenite goes into a single phase like a reset button based on figure 5. Based on figure 5, the grain sizes of austenite are all equal. To achieve favourable results, melting of the metal must be neglected, where to control the temperature and time when the annealing process is going on.
In this research and experiment, to implement and gain accuracy of results, having a temperature for reference where the stainless steel is in a single phase which is austenite. Any temperature is chosen ranging from 950°C to 1230°C, which is the best temperature for annealing. Having a single phase is to decrease and avoid any errors if possible, having the result to more accurate and decreasing the deviation between the samples. In this case taking the annealing process for each sample to reach the temperature of 1050°C.
Based on the research done by S.A.Tukur, M.S Dambatta, A.Ahmed, N.m. Mu’az on effect of heat treatment temperature on mechanical properties of the AISI 304 stainless steel, where annealing process increases the hardness of the material. From the data sheet where the steel reaches 1090°C, the hardness value increases from 20.4HRC to 24HRC. The hardness value is measured in the unit of Hardness, Rockwell C. Since 20.4 HRC is not at room temperature, by taking the value of Hardness, Rockwell B from the mechanical properties of the stainless steel, which gives 70 HRB. Where HRB is converted to HRC to be compared. Using the conversion, where 70HRB gives 0 value of HRC. In this case 100 HRB is equal to 24 HRC and between 97HRB and 98HRB gives roughly 20.4 HRC. From the data given the hardness of stainless steel increases. Where the hardness increases, the stainless steel has entered the austenite phase. Beyond the temperature of 1190°C, the stainless steel was analysed where the hardness values starts to decrease. Based on the experimental values done by the researches, the graph is plotted in the figure below;
Figure 7: Variation of Hardness Value under Increasing Temperature
(Source: Effect of Heat Treatment Temperature on Mechanical Properties of the AISI 304 Stainless Steel)
2020-4-9-1586422118