Effect of Nitriding Voltage on the Impact Load Fatigue and Fracture Toughness Behaviour of CoCrMo Alloy Nitrided Utilising a HIPIMS Discharge

CoCrMo alloy specimens were plasma nitrided using a High Power Impulse Magnetron Sputtering (HIPIMS) discharge. In this work the effect of nitriding voltage (-700 V to -1100 V) on the microstructure, surface hardness, impact load fatigue resistance and fracture toughness (KIc) of the alloy has been investigated. Results revealed that the specimens treated at lower nitriding voltages (-700 V and -900 V) develop a nitrided layer consisting a mixture of Co4N+Co2-3N phases. As the nitriding voltage increased (-1000 V and -1100 V), this transformed into a thick layer consisting mainly of Co2-3N with a minor contribution from CrN/Cr2N phases. Accordingly, surface hardness tests after nitriding showed a significant improvement in hardness value (H= 23 GPa) as compared to the untreated specimen, (H= 7.9 GPa). The impact resistance of the alloy also increased with the nitriding voltage. Impact crater profiling of the specimens subjected to impact load tests showed that the depth of the crater decreased significantly, 2 especially at higher nitriding voltages. At the end of the impact load test (one million impacts), the crater depth for an untreated alloy (12.78 μm) was found to be twice to the crater depth measured for the specimen nitrided at -1100 V (7.1 μm). Impact testing results indicate that the fatigue endurance limit of the CoCrMo alloy increased steadily and considerably with the increase of the nitriding voltage. HIPIMS plasma nitriding resulted in a layer material with improved plain strain fracture toughness (KIc), with higher values (KIc) = 1011 MPamm1/2 (-700 V specimen) were calculated as compared to KIc = 908 MPamm1/2 for the untreated specimens. Critical material parameter ratios such as H/E (elastic index or elastic strain to failure) and H3/E2 (plastic index) of the nitrided layers were calculated using surface hardness (H) and elastic modulus (E) values obtained with the help of nanoindentation tests. Systematic improvement in the values of H/E and H3/E2 ratios calculated for all nitrided specimens validated the increase in fracture toughness and impact load fatigue resistance of the nitrided specimens as compared to the corresponding properties of the untreated CoCrMo base alloy

Immunoglobulin Genomics in the Guinea Pig (Cavia porcellus)

In science, the guinea pig is known as one of the gold standards for modeling human disease. It is especially important as a molecular and cellular biology model for studying the human immune system, as its immunological genes are more similar to human genes than are those of mice. The utility of the guinea pig as a model organism can be further enhanced by further characterization of the genes encoding components of the immune system. Here, we report the genomic organization of the guinea pig immunoglobulin (Ig) heavy and light chain genes. The guinea pig IgH locus is located in genomic scaffolds 54 and 75, and spans approximately 6,480 kb. 507 VH segments (94 potentially functional genes and 413 pseudogenes), 41 DH segments, six JH segments, four constant region genes (μ, γ, ε, and α), and one reverse δ remnant fragment were identified within the two scaffolds. Many VH pseudogenes were found within the guinea pig, and likely constituted a potential donor pool for gene conversion during evolution. The Igκ locus mapped to a 4,029 kb region of scaffold 37 and 24 is composed of 349 Vκ (111 potentially functional genes and 238 pseudogenes), three Jκ and one Cκ genes. The Igλ locus spans 1,642 kb in scaffold 4 and consists of 142 Vλ (58 potentially functional genes and 84 pseudogenes) and 11 Jλ -Cλ clusters. Phylogenetic analysis suggested the guinea pig’s large germline VH gene segments appear to form limited gene families. Therefore, this species may generate antibody diversity via a gene conversion-like mechanism associated with its pseudogene reserves