Yang Alternatives to hard chromium plating on piston rods Degree Project of 30 credit points
As a main part of hydraulic cylinder, the piston rod is used in tough surrounding and corrosive condition; consequently a high quality protecting layer is essential. Currently EHC, electroplating hard chromium (hard chrome) is a widespread method for piston rod due to powerful performance and low cost. Unfortunately the plating process contains hexavalent chromium (Cr) which is toxic and carcinogenic; perhaps it will be prohibited in the nearing future. Therefore it is crucial to seeking alternatives to hard chrome for piston rod manufacturer. Through extensive searching for alternatives to hard chrome, the competitors like HVOF, electroplating tungsten plating and stainless steel linear were studied in the present work. Since microhardness and corrosion resistance are top priorities, after comparison perhaps Cr3C2-NiCr20% HVOF is the most promising technique. Distinct pretreatments Cr3C2-NiCr coatings were compared with hard chrome in pendulum impact test, hardness test and acetic acid salt spray (AASS) test. The results indicate that hard chrome show higher toughness more than 40% compare with HVOF, the microhardness of HVOF is higher than hard chrome, mean value 1784 Vs. 1244 HV and both coatings have excellent bonding strength. After 40 hours in AASS test, the hard chrome was rated No. 10, however the HVOF just No. 6.
Microstructural characterization and abrasive wear performance of HVOF sprayed Cr3C2-NiCr coating
Abstract Cr 3 C 2 –NiCr coatings were deposited by high velocity oxy-fuel (HVOF) process with different spray parameters to examine dominant microstructural factors in abrasive wear of the coatings. The microstructure of the HVOF sprayed Cr 3 C 2 –NiCr coatings was characterized by scanning electron microscopy and transmission electron microscopy (TEM). The apparent average size and volume fraction of carbide particles in the coatings were estimated through a quantitative imaging analysis. The formation of carbide phases in the coating was discussed based on the TEM observation results. The abrasive wear behavior of the coating was evaluated by the dry rubber wheel abrasive wear test and the wear mechanisms were elucidated. Influences of apparent size and volume fraction of carbide particles on the abrasive wear weight loss were examined through correlating the proposed relation with the experimental results. Results showed that Cr 3 C 2 particle size was significantly reduced after the spraying and Cr 7 C 3 carbide was present around Cr 3 C 2 particles, and Cr 23 C 6 carbide was dispersed in NiCr alloy matrix with a nano-crystalline structure. The three carbides were formed in the coating through different mechanisms. The removal of carbide particles in the coating was mainly responsible for the abrasive wear of the coating. The content and particle size of the Cr 3 C 2 carbides were the two key factors controlling the abrasive wear of the HVOF sprayed Cr 3 C 2 –NiCr coatings.
An anionic shell shields a cationic core allowing for uptake and release of polyelectrolytes within core-shell responsive microgels.
To realize carriers for drug delivery, cationic containers are required for anionic guests. Nevertheless, the toxicity of cationic carriers limits their practical use. In this study, we investigate a model system of polyampholyte N-isopropylacrylamide (NIPAM)-based microgels with a cationic core and an anionic shell to study whether the presence of a negative shell allows the cationic core to be shielded while still enabling the uptake and release of the anionic guest polyelectrolytes. These microgels are loaded with polystyrene sulfonate of different molecular weights to investigate the influence of their chain length on the uptake and release process. By means of small-angle neutron scattering, we evaluate the spatial distribution of polystyrene sulfonate within the microgels. The guest molecules are located in different parts of the core-shell microgels depending on their size. By combining these scattering results with UV-vis spectroscopy, electrophoretic mobility and potentiometric titrations we gain complementary results to investigate the uptake and release process of polyelectrolytes in polyampholyte core-shell microgels. Moreover, Brownian molecular dynamic simulations are performed to compare the experimental and theoretical results of this model. Our findings demonstrate that the presence of a shell still enables efficient uptake of guest molecules into the cationic core. These anionic guest molecules can be released through an anionic shell. Furthermore, the presence of a shell enhances the stability of the microgel-polyelectrolyte complexes with respect to the cationic precursor microgel alone.