Issue 22

H. Singh et alii, Frattura ed Integrità Strutturale, 22 (2012) 69-84; DOI: 10.3221/IGF-ESIS.22.08 80 Effect of temperature on DE The other important parameter is the particle and substrate temperatures; as the air temperature in the pre-chamber increases, both the particle velocity and the particle and substrate temperatures increase which effects the deposition efficiency, as higher deposition rate of Cu particles was noticed for higher substrate temperature, even under the condition where particles were kept at room temperature [7]. The increase in deposition efficiency is reported by Li et al. [13] with increase in temperature of carrier gas. During study on titanium powder, no particle deposition occurred for temperature of nitrogen gas below 155 o C and the deposition efficiency increased quickly, especially when the nitrogen temperature becomes higher than 215 o C [13]. Lima et al. [10] noticed no change in the deposition efficiencies with the rise of gun temperatures from 370 to 480 o C, for Ti coatings on Al pipes. Effect of surface condition on DE It has also been reported by Ghelichi et al.[7] that with a greater roughness of the substrate surface (going from polished to grit-blasted), deposition efficiency of metallic powders increases because the impacting particles get deformed more severely on roughened surface as compared to smooth surface of the substrate, which enhanced the mechanical interlocking. Kumar et al. [24] suggests that the substrate roughness whose crest size is same as particle size and the trough size is half the particle size creates better bonding. Hence, the bond strength values for grit-blasted substrates are higher. So, during cold spray process to improve adhesion, sand blasting is commonly used like other thermal spraying. However, in this spraying process, during delay time the surface is exposed to a large number of particle impacts before particles start to adhere to the surface. So these impacts of the sprayed particles can play an important role for preparation and activation of the substrate surface and this effect can be used in replacing the sand blasting, where it is unacceptable like in spraying on parts with thin walls, parts already coated and parts made of brittle materials and also the effect of interface contamination due to penetration of sand blasting particles into the substrate, especially for soft substrate materials can be avoided [7]. Kumar et al. [24] also suggests the need of further research to optimize the roughness value for different materials. A PPLICATIONS OF CS old spray technology is not here to replace any of the well-established thermal spray methods. Instead, cold spray technology is expected to supplement and expand the range of applications for thermal spray [1]. CS applications include both production and restoration [6] in the field of medical, aerospace, electronics, automotive and petrochemical industries [25]. Any defect may be easily removed by this process to save production quality. One of the important applications is the repair of the casting defects. Both casting defects and machining defects removal by this process can save small-batch or unique production. Also casting moulds restoration or modification become easy with this process.  CS is also widely used for the restoration of antique objects both technical as cars and airplanes, and art as metal sculptures [6]. It is used in aerospace industry for aluminum and aluminum alloy coatings for repair/refurbishment of space shuttle solid rocket boosters, in aircraft industry for repair and retrieval of parts and plate stocks used in aircraft structures, repair/refurbishment of casings in gas turbines, corrosion protection coatings in petrochemical, and anti skid coatings [2], sealing up the leakages, shape restoration, defects elimination at small automotive workshops, like repair of vehicle platforms [6]. It is also used for spraying of copper alloys on 'touch' surfaces which are frequently in human contact, such as door knobs, light switches, faucets, bed rails, food preparation areas and other hardware[25]. The continuous seamless titanium pipes can be directly manufactured using Cold Spray coating technique.  CS coatings are successfully applied to welding lines after the welding of hot galvanized metal structures, anti seizure coatings coats the screws at oil-well tubing and at marine ship propeller shaft. This process is also used for unique coatings to special heating glasses for ships, airplanes and railroad locomotives. Also elements of optical electronic devices are created by cold spray[6]. The restoration of defected or worn bearing seats by this process allows avoiding the replacement of the scarce or expensive parts. It is also used to remove defects at the surfaces of the huge rolls for paper and polyethylene film production. Hence, the service of worn and old equipment becomes much easy and simple with the use of cold spray process[6].  Cold spray technique is used to fabricated the Al-tube heat exchanger, used as air conditioning equipments for all types of vehicles these days. It is observed by Yoon et al.[26] that high quality coating, which has high corrosion resistance with good brazeability as compared to conventional methods can be obtained by CS process and also with less manufacturing cost. C