NISCAIR Online Periodicals Repository Collection: IJEMS Vol.17(1) [February 2010]

Metallurgical analysis of burst tested aluminium alloy AA 2219 miniature assembly

Title: Metallurgical analysis of burst tested aluminium alloy AA 2219 miniature assembly

Authors: Jha, Abhay K; Diwakar, V; Sreekumar, K

Abstract: A miniature assembly fabricated from aluminium alloy AA 2219 forging and 2.0 mm thick sheets is subjected to burst test using a pressure cartridge at very high strain rate of loading. The microstructural features associated with deformation at high rate of loading using explosive energy is analyzed by optical and scanning electron microscopy (SEM). The microstructures consisted of adiabatic shear bands formed in an extremely short time by the combined effects of the highly localized shear deformation and the high temperature rise that occurred within the shear bands. Scanning electron microscopy revealed features of melting within the adiabatic shear band. This paper highlights the details of experiment carried out and the salient observations at microscopic level on the fracture surfaces taken from the test article.

Page(s): 67-71

Mechanoluminescence technique for real-time monitoring of cracks produced during application of loads on crystals

Title: Mechanoluminescence technique for real-time monitoring of cracks produced during application of loads on crystals

Authors: Chandra, B P; Mahobia, S K; Nema, S K; Jha, P; Kuraria, R K; Kuraria, S R

Abstract: When a load is applied on to a crystal, then the fracto- mechanoluminescence (ML) emission takes place in the form of light pulses. The number of ML pulses and the time duration t_c for the appearance of ML increase with increasing value of the load and the average ML intensity from a single ML pulse decreases with increasing value of the load. For a given value of the applied pressure, the total number N_Tof ML pulses, the total ML intensity I_T and the time duration t_c of ML emission increase with increasing size of the crystals. As the total ML intensity is directly related to the area of newly created surfaces, the pressure dependence of the total ML intensity indicates that initially the total area of newly created surfaces increases with increasing value of the applied load and later on it tends to attain a saturation value for higher values of the applied load. As the strain rate is maximum at a particular time after the application of load on to a crystal, the rate of the emission of ML pulses is maximum at a particular time after the application of load on to the crystals. The dependence of N_T, I_T, and t_c on the applied pressure P_ofollows the following expressions, respectively N_T = M_o V^y [1 – exp{–δ_c (P_o – P_f)}] I_T = D b M_o V [1 – exp{–δ_c (P_o – P_f)}] and, t_c=1/αln( P₀/P_f) where V is volume of crystal, y is an exponent, δ_c =1/P_c, P_c is the critical pressure, P_fis the fracture stress, M_o, D, b, and α are constants. A good agreement is found between the theoretical and experimental results.

Page(s): 61-66

Densification behaviour of Al-Pb alloys –A study of effect of certain process parameters

Title: Densification behaviour of Al-Pb alloys –A study of effect of certain process parameters

Authors: Sastry, ChV S H S R; Janardhana, G Ranga

Abstract: The recent research into the alternate sliding bearing materials unequivocally point to the beneficial role of lead in aluminum. But, these alloys offer a manufacturing challenge, due to wide immiscibility gap. For sliding bearing applications, controlled porosity (size, distribution and nature) is an important consideration, as it influences the tribological performance through mechanical properties and spreading of lead in aluminum matrix. In the present investigation, the effects of alloy composition, ball to charge ratio and mixing/milling route on densification behaviour of Al-Pb alloys processed through conventional ball milling and attrition milling routes, using XRD, SEM and compressibility test are studied. The resulting morphological changes of powder complexes are examined, on five compositions of alloys to determine compaction response. The study concludes that attrition milling is an effective method for densification of experimental alloys.

Page(s): 56-60

Investigation into the densification of AISI304 parts fabricated by hybrid powder metallurgy techniques

Title: Investigation into the densification of AISI304 parts fabricated by hybrid powder metallurgy techniques

Authors: Lu, Z L; Liu, J H; Shi, Y S; Li, D C

Abstract: Complex and high-performance parts of metal and ceramics can be fabricated by selective laser sintering/isostatic pressing (SLS/IP), in which cold isostatic pressing (CIPing) is introduced into SLS followed by high sintering (HSing) and hot isostatic pressing (HIPing). In this paper, the mechanisms of action of CIPing pressure and HSing temperature on relative densities of AISI304 parts fabricated by SLS/IP are respectively investigated. Based on the liquid sintering theory, the effects of trace FeB on their relative densities, metallurgical structures and mechanical performances are likewise analyzed. Results show that there is a minimal threshold of CIPing pressure for AISI304 parts in the process of SLS/IP, which is about 400 MPa. Their relative densities approximates certain value with an increase of HSing temperature from 1250°C to 1350°C, which are improved while their mechanical performances worsen with an increase of FeB content from 0.5% to 5.0%, and their metallurgical structures consist of eutectic (α-Fe, Fe₂B) and (Ni,Ni₃B) besides austenite (Fe,Cr,Ni,C). Although their strengths are better when FeB content is 0.5wt%, their elongation percentages are lower, which is only about 8%.

Page(s): 49-55