The objective of this project is to study the homogeneity, compressibility and sintering of the powder mixture

The aim of this project is to study the homogeneity, compressibility and sintering of the powder mixture. The homogeneity of the mixture was determined using a scanning electron microscope (SEM), while the compressibility of the mixture was determined based on the produced compressibility curve. FLN4-4405 in sintered and heat treated condition. 6 Table 2.2 FL-4405HT Rotating Beam Fatigue Endurance Limit (Mpa).

This process is suitable for many applications due to the availability of a wide range of powder production, the ability to produce parts in net dimensions (net shape formation) and overall economy of operation.

Problem Statement

Problem Identification

Significant of the Project

Objective and Scope of Study

The Relevancy of the Project

Feasibility of the Project within the Scope and Time Frame

Extra Fine Nickel Powder

The FEL of Ni-containing alloys was more than 10% higher than the base FL-4405 alloy in the heat-treated condition. The cutectoid in the sintered microstructure of FL-4405 steel has relatively coarse carbide plates with hardly soluble ferrite. Addition of extra fine nickel powder results in the formation of martensitic Ni-rich phases in the sintered microstructure (see Figure 2.4).

Extra-fine Ni-rich phases are more uniformly distributed in the sintered steel than with the standard Ni powder.

Figure 2.1: Standard Ni powder [4]

Graphite Powder

Methods of Powder Production

• Atomization
• Gas Atomization
• Water Atomization
• Centrifugal Atomization
• Oxide Reduction
• Electrolytic Deposition
• Carbonyls
• Mechanical Communition
• Mechanical Alloying
• Other Methods

At the core of water atomization, high-pressure water jets are directed against the melt stream, forcing the disintegration of the melt into droplets that solidify into irregular shapes. The consumable electrode must be made of the desired alloy, since there is no alloy in the thin melt layer at the end of the electrode. When made from brittle materials, the powder particles have angular shapes, while when made from ductile metals, they are flaky and not particularly suitable for powder metallurgy applications [2].

Metal powders are produced using high-temperature processing techniques based on the reaction of volatile halogens (a halogen compound and an electropositive element) with liquid metals and the controlled reduction and reduction/carburization of solid oxides [2].

Powder Characterization .1 Particle Size

Particle Shape

Because particle shape measurement is difficult, qualitative descriptors are used to convey particle shape. This is because usually the shape of the particles is irregular and the cross-section can have large variations in the pore structure [6].

Particle Packing and Flow

Mixing Metal Powders

Compaction

The particle shape, mean size and size distribution dictate the packing density of the loose powder. But a compact made from such a powder has poor green strength, and, therefore, such a powder is unsuitable for P/M parts that are made by the pressing method. For the production of P/M parts, powders with some irregularity in shape are preferred, although the packing density of the powder in the head is somewhat lower than that of the spherical powder.

In order to reproduce the dimensions of the part, the powder filling density must be consistent from one batch of powder to the next. The density after compaction (green density) depends primarily on the compaction pressure, the metal powder composition and the hardness of the powder. The higher the density, the higher the strength and modulus of elasticity of the part.

The reason is that the higher the density, the higher will be the amount of solid metal in the same volume; therefore the greater will be the part's resistance to external forces. Due to friction between the metal particles in the powder and between the punch and the die walls, the density can vary significantly within the part. The compaction pressure required depends on the properties and shape of the particles, the methods of mixing and the lubrication.

Press selection depends on the size and configuration of the part, density requirements and production rate. The higher the compression speed, the greater the tendency to trap air in the die cavity.

Sintering

Proper control of the furnace atmosphere is essential for successful sintering and obtaining optimal properties. For the same volume of inclusions, the smaller inclusions have a greater effect because there are more of them per unit volume of the part. The gases most commonly used for sintering a variety of other metals are hydrogen, dissociated or combusted ammonia, partially combusted hydrocarbon gases and nitrogen.

Sintering mechanisms are complex and depend on the composition of the metal particles and the processing parameters. As the temperature rises, two adjacent particles begin to form a bond by diffusion (solid-state bonding), as shown in Figure 2.11 below. As a result, the strength, density, ductility, and thermal and electrical conductivity of the compact increased.

At the same time, however, the compact is shrinking; so allowance must be made for shrinkage. Metal atoms will be released into the vapor phase of the particles because the material is heated very close to its melting temperature. At convergent geometries (the interface of two particles), the melting temperature is locally higher, and the vapor solidifies again; thus the interface grows and strengthens, while each particle as a whole shrinks.

If two adjacent particles are of different metals, alloying can occur at the interface of the two particles. Depending on temperature, time and processing history, different structures and porosities can be obtained in a sintered compact.

Figure 2.10: Components in a furnace [11]

METHODOLOGY

Procedure Identification Mixing

When producing the samples using powder metallurgy technique, firstly before mixing, microstructure images of the loose powders (nickel powder and graphite powder) are determined using SEM. Second, both powders are mixed by hand with a binder (2.02 wt %) which is phenolic thermosetting powder to bond nickel powder and graphite powder together. Next, compaction process; where the mixture is pressed into molds using presses that are either hydraulically or mechanically driven.

A graph of Pressure, P vs Green Density, ρ is shown where the green density is determined using the formula ρ=m/v. Microstructure images of the sintered pallet are determined using SEM and the plot of Pressure, P vs Green Density, ρ is plotted.

Tools Required

An auto pallet press machine is used to press the mixture into shapes in a controlled variable die. A grinder is a machine tool used to produce very fine finishes or very light cuts, while a polisher is a machine tool that produces a smooth and shiny surface by rubbing or chemical action, leaving the surface with considerable specular reflection and minimal diffuse reflection [ 5]. ]. A balance (analytical balance) is an instrument used to measure mass with a very high degree of accuracy.

The weighing pan(s) of a high precision analytical balance (0.01 mg or better) are inside a transparent cabinet with doors so that dust does not collect and any airflow in the room does not affect the delicate balance [5]. Scanning electron microscope (SEM) is a microscope that produces an image by using an electron beam that scans the surface of a sample, where an image is produced by reflected electron beams. Hardness Testing Machine is a machine that determines the hardness by measuring the penetration depth of an indenter under a large load compared to the penetration made by a preload [5].

Figure 3.3: Mortar Grinder

Material Selection

Furthermore, the student has determined the particle shapes in both powders using SEM in order to know the processes by which they are produced. In the case of nickel powder, the particle shape obtained is rounded, and therefore the powder is produced via atomization and chemical decomposition process (see Figure 4.3). Furthermore, graphite powder is irregular in shape; therefore, graphite powder is produced by atomization and chemical decomposition process (see figure 4.4).

As referred to in Table 4.1 below, the minimum solubility of Ni-C mixture is 0.02 wt.% while the maximum solubility of Ni-C mixture is 0.2 wt. Consequently, the student determined the optimum solubility of carbon (additive) which is 0.1 wt.% and mixes with the rest 99.9 wt.% nickel (base powder).

Figure 4.2: Graphite Powder (additive)

Mixing

As referred to the purpose of mixing, the student has determined the uniformity/homogeneity of the mixture using SEM. The student has completed the compaction process by producing 6 pallets with different compaction forces acting on them for 2 minutes (compression time). The student has used the Vanier Caliper to measure the dimension (see figure 4.11). The details of the dimension of each pallet are described in Table 4.2 below.

From the above table, the student concluded that the green density for each pallet can be achieved. This is done by using the simple formula ρ = m/v, where ρ is density, m is the mass of the pallet and v is the volume of the pallet. The mass of the pallet can be obtained by using balancing beam, while the volume of the pallet can be obtained by calculating, π x (d/2) x (h).

As shown in Table 4.3, the student concluded that the pallet begins to have constant density at force 80067.99N. In addition, the student has determined the microstructure image of the green compact using SEM as shown in Figure 4.13 below. This device works by emitting electrons into the gaseous volume, thus generating additional ionization and avalanche amplification [5].

As we refer to the figure below, the carbon dust covered the nickel dust and also exists in the middle of the nickel to nickel contact.

Figure 4.7: Uniformity/homogeneity of the mixture

Sintering

By inserting the mass of sample coated in air (A) and sample mass coated with distilled water (B) into the equation above, the results of the sintered densities for each pallet are described in Table 4.6 below. As observed from the table above, the student concluded that the pallet begins to have constant density at force 80067.99N (Pallet 5). In addition, the student has determined the microstructure image of the sintered mixture using SEM as shown in Figure 4.17 below.

After completing the 3 main processes in P/M techniques, the pallets must be tested under hardness testing machine. The results and results of the tests will be discussed under Subtopic 4.6 (Hardness Tests).

Table 4.5: Mass measured prior to different conditions Table 4.5: Mass measured prior to different conditions

Hardness Test

The strength of the sample pallet increases with the increase in force exerted during compaction. However, the reading for pallet number 6 is much preferable because it has reached steady state. Pallet number 5 reached slightly steady state, but for safety factor the student chose pallet 6 (refer to chart on previous pages).

Table 4.7 shows the result obtained from the hardness measurement using Rockwell Hardness Test

CONCLUSION

APPENDICES