Surface engineering is a discipline in materials science that is involved in the surface of materials. It is mainly used to enhance the performance of materials. Some of the examples of surface engineering include shot peening, carburisation, surface texturing and use of coatings.
Below are examples of components in military aircrafts where the concept of surface engineering has been applied.
Example 1
An example of a component of a military aircraft that uses surface engineering is the ball bearings. Ball bearings in military aircraft are used all over the aircraft design and the frame of the aircraft. The ball bearings are made of 440c stainless steel because of the various advantages offered by the material that will be explained below.
The ball bearings are made from the steel because of the material properties offered which make it a suitable metal to be used. Firstly, the stainless steel has a very high resistance to corrosion making it appropriate to be used under any harsh environmental situations which the aircraft is operating under. Secondly, the material has a very high specific strength and this gives the ball bearings a very durable structure. Hence, making the military aircraft bearings to oscillate and spin well at a range of rotating and oscillating velocities without any damage.
The surface engineering method used for the ball bearing is carburising and to be specific, low pressure vacuum carburising. The process is executed in a furnace vacuum. After the furnace has been charged, it is evacuated and pressure is applied until the pressure reaches ten Pascals. The charge is then heated in temperature ranges of 790 to 1040 degrees Celsius in up to 3 stages. The first stage starts with putting a hydrocarbon into the evacuated furnace. The carbon induced diffuses into the ball bearings. When the depth required has been attained, the temperature is decreased to the temperature of hardening and gas is used to quench the charge. Lastly, the bearings are heated at temperature ranges of five degrees and the bearing will be carburized. Carburising is limited to metals that have high melting points because the process is undertaken under high temperatures and that why steel is used.
The performance of the ball bearing will be improved since the material will be harder than before. When the ball bearings are harder they become more durable and their strength is improved. The carbon produced by the hydrocarbon used in the process penetrates the surface of the steel and thus hardening it.
A research paper from the link http://www.sciencedirect.com/science/article/pii/S0924 013612001070 looks at the effect of orientation of components and carburising on the distortion of martensitic steel. The aim of the research is to examine the effect of the carburisation process on the distortions that happen when martensitic sheet made from steel are quenched. The results of the research paper indicate that the least distortion that arose during the quenching of the uncarburised sheets was limited to only closing and opening of the wall angle of the channel. Another indication from the results is that the selective carburising on a specified channel surface causes a considerable alteration in the structure of the sheet during the quenching process, which is associated with the carburizing depth. The results discussed above can have a lot of applications in the transport sector. From the results, selective carburising causes an increased carburising depth. Increased carburising depth lead to improved hardness of steel .This knowledge can be used to make the bodies of transport vessels to be stronger. Also least distortion occurrence indicates a reduced residual stress and less cracks in the steel sheets. This knowledge can be used in the transport sector in developing components of a transport vessel e.g. ball bearings that can be employed in adverse weather environmental conditions.
Example 2
Another component in the military aircraft sector applies the shot peening process of surface engineering is the landing gear. This is the equipment that enables the plane to land securely and successfully and also it is used to support the plane when it is at rest. The main materials that are used in the manufacture of landing gear include ultra-high tensile steels (UHTS) and aluminium alloys.
The military landing gears are manufactured from low alloy steels since they are cheap and also result in improved better fatigue strengths; however, they are vulnerable to corrosion and need the use of surface engineering methods, for example, anodization and use of coatings that protect from corrosion(http://www.lambdatechs.com/landinggear.pdf). Due to the high strength of the landing gear, the planes are able to land on any grounds that also include bare soils.
The surface engineering process that is used in the process of manufacture of aircraft landing gear is the shot peening process. This is a cold work process that is used in metal finishing so as to avoid stress and fatigue corrosion failures and also to ensure that the life of the part is extended. This process involves a small spherical shot that strikes the surface of the part that should be finished. The dimples the surface resulting in formation of compression stresses. As more strikes are applied, multiple overlapping dimples are formed throughout the metal surface. The surface compression stress enables the strength of the metal to be improved; therefore the finished part can resist corrosion fatigue and cracking, fatigue failures, and galling and erosion from cavitation.
The shot peening process improves the performance of the landing gear because it definitely improves the fatigue life of the ultra-high tensile steel. This means that military aircrafts can have a longer period of use. Also, this process results in use of less weight of material and corrosion resistance.
A research paper on the Fatigue Life Enhancement of AluminiumAlloy for Aircraft by Fine Particle ShotPeening (FPSP) from the link; http://www.sciencedirect.com/science/article/pii/S0924 013611000744, describes the shot peening process. The aim of this research paper is to investigate whether the use of small ceramic particles and high blowing velocity of media will result in an aluminium alloy that has better fatigue life than the process that uses the conventional shot peening process. In the transport sector, the fine particle shot peening process could be relevant in the transport sector because; firstly, it is faster than the conventional shot peening process since there is use of high velocity media. Secondly, the fine particle shot peening process results in products that have higher fatigue failure periods as compared to those that have been subjected to conventional shot peening process. The greater fatigue property remains the same after the process of anodization which imparts the property of corrosion protection. Thirdly, this method of shot peening does not need the process of removal of iron. This process results in the reduction of the weight of transport materials.
