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Öğe DÖKÜM VE EKSTRÜZYON SONRASI YAŞLANDIRILMIŞ CA, SR, SN VE ZN KATKILI MG-Y-ND (WE43) ALAŞIMLARININ TRİBOLOJİK VE KOROZİF ÖZELLİKLERİNİN İNCELENMESİ(2022-06) Keskin, EsmaBu çalışmada, düşük basınçlı döküm yöntemi ile üretilen Mg- Y- Nd sistemli (WE43) magnezyum alaşımlarına %0.5 ve %1 oranlarında Ca, Sr, Sn ve Zn alaşım elementleri katılmıştır. Üretilen bu alaşımlara döküm ve ekstrüzyon sonrası yaşlandırma işlemi uygulanmıştır ve karşılaştırmalı olarak faz morfolojisi, sertlik, aşınma ve korozif özellikleri incelenmiştir. Alaşımlar, SF6+CO2 koruyucu gaz kullanılarak 775°C pota sıcaklığında düşük basınçlı bir döküm ünitesinde gerçekleştirilmiştir. Alaşımlama işlemi tamamlandıktan sonra eriyikler 2 bar basınç altında metal döküm kalıbına dökülerek numuneler elde edilmiştir. Magnezyum alaşımlarının üretimi esnasında oluşabilecek segregasyonları en aza indirmek ve alaşım elemanlarının homojen dağılımı sağlamak için ekstrüzyon işleminden önce homojenizasyon işlemi (525 °C, 8 saat) yapılır. Ekstrüzyon işlemi 350°C sıcaklığında, 30 mm yüksekliğinde ve 32 mm çapındaki numunelerin 16:1 ekstrüzyon oranı ve 0,3 mm/sn. zımba hızında preslenmesi ile yapılmıştır. Döküm ve ekstrüzyon işlemi gerçekleştirilen magnezyum numuneleri çözeltiye alma (525°C, 8 saat) ve suni yaşlandırma (250°C, 32 saat) olmak üzere iki aşamadan meydana gelen yaşlandırma işlemi uygulanmıştır. Daha sonar döküm ve ekstrüzyon sonrası yaşlandırılmış numunelere mikroyapı, aşınma ve korozyon deneyleri yapılmıştır. Döküm sonrası yaşlandırılmış katkısız WE43’te yapılar ?-Mg tanelerinden oluşmuştur ve çökelme sertleşmesi sonucu tane yapıları büyük ve çökeltilerinin tane içi ve tane sınırlarındadır. Alaşım elementleri katkısı ile sırasıyla mikroyapı; kalsiyum ile tane inceltici bir şekilde kendini göstermiştir ve stronsiyum ile tanelerde büyüme ve tane yüzeylerinde dentritik yapılar gözlemlenmiştir. Kalay katkısı ile Sn3Y5 intermetaliği tane içleri ve tane yüzeylerinde dentritik yapı formunda görülmektedir. Artan çinko katkısı ile tanelerdeki büyüme daha düzenli ve sıkı bir faz morfolojisini almıştır. %1 Zn katkısı ile Mg-Zn-Y intermetalikleri ?- Mg fazlarını tane sınırları boyunca kuşatmıştır. Ekstrüzyon sonrası çökelme sertleşmesi uygulanması durumunda tüm alaşımlarda ekstrüzyon yönünde tane yapıları daha küçük, eş eksenlidir ve intermetalikler tane sınırlarında birikmiştir. Sertlikteki artış hem alaşım elementleri hem de çökelme sertleşmesi ile olmuştur. Korozyon sonuçlarına göre ekstrüzyon ardından uygulanan çökelme sertleşmesi durumunda ağırlık kayıpları döküm sonrası çökelme işlemine kıyasla daha azdır. Bununla birlikte, en iyi korozyon davranışını çinkolu alaşım, en kötüsünü kalsiyumlu alaşım göstermiştir. Aşınma sonuçlarına göre ekstrüzyon ardından uygulanan çökelme sertleşmesi durumunda ağırlık kayıpları döküm sonrası çökelme işlemi durumuna göre daha azdır ve aşınma sonuçları sertlik sonuçlarına parallel olarak gittiği saptanılmıştır ve çinko katkılı alaşımın diğer alaşım elementlerine kıyasla aşınma direncinin daha iyi olduğu görülmüştür.Öğe Effect of 0.20% Beryllium (Be)-Added CuAl₁₀Ni₅Fe₄ Alloy on Tribological Behavior and Microstructural Properties After Post-Casting Heat Treatment and Forging Process(MDPI AG, 2024-11-25) Khaled A. A. Babay; Esen, Ismail; Sagiroglu, Selami; Ahlatci, Hayrettin; Keskin, EsmaThis study explored how post-casting heat treatment and forging affected the tribological and microstructural characteristics of 0.20% beryllium (Be)-added CuAl₁₀Ni₅Fe₄ alloys. The heat-treated CuAl₁₀Ni₅Fe₄ microstructure exhibits a copper-rich α (alpha)-solid-solution phase, a martensitic β (beta)-phase, and diverse intermetallic κ (kappa)-phases, such as leaf-shaped κI, thin κIII, and black globs. Adding 0.20% beryllium to CuAl₁₀Ni₅Fe₄ alloys enhanced the dendritic arm thickness, needle-like shape, and κ-phase quantities. Significant κIV- and κII-phase precipitation was observed in the tempered β-phase. Beryllium improves the aluminum matrix’s microstructure. Forging greatly reduced the microstructural thickness of CuAl₁₀Ni₅Fe₄ and CuAl₁₀Ni₅Fe₄-0.20% Be alloys. The forging process also developed new κIV-phases. Wear resistance and hardness improved with beryllium. The CuAl₁₀Ni₅Fe₄-0.20% Be alloy had the highest hardness values (235.29 and 255.08 HB) after solution treatment (ST) and tempering (T) after casting and forging (F). The CuAl10Ni5Fe4-0.20% alloy with Be added had the best wear after solution treatment, tempering, and forging. The CuAl₁₀Ni₅Fe₄-0.20% Be alloy demonstrated a 0.00272 g weight loss, a 1.36 × 10−8 g/N*m wear rate, and a 0.059 friction coefficient at 10,000 m after forging (F).Öğe Effect of Oxidation Process on Mechanical and Tribological Behaviour of Titanium Grade 5 Alloy(Mdpi, 2024) Saier, Abdulsalam; Esen, Ismail; Ahlatci, Hayrettin; Keskin, EsmaIn this study, microstructural characterization, mechanical (tensile and compressive) properties, and tribological (wear) properties of Titanium Grade 5 alloy after the oxidation process were examined. While it is observed that the grey contrast coloured alpha grains are coaxial in the microstructures, it is seen that there are black contrast coloured beta grains at the grain boundaries. However, in oxidised Titanium Grade 5, it is possible to observe that the alpha structure becomes larger, and the number and density of the structure increases. Small-sized structures can be seen inside the growing alpha particles and on the beta particles. These structures are predicted to be Al-Ti/Al-V secondary phases. The nonoxidised alloy matrix and the OL layer exhibited a macrolevel hardness of 335 +/- 3.21 HB and 353 +/- 1.62 HB, respectively. The heat treatment increased Vickers microhardness by 13% in polished and etched nonoxidised and oxidised alloys, from 309 +/- 2.08 HV1 to 352 +/- 1.43 HV1. The Vickers microhardness value of the oxidised sample was 528 +/- 1.74 HV1, as a 50% increase was noted. According to their tensile properties, oxidised alloys showed a better result compared to nonoxidised alloys. While the peak stress in the oxidised alloy was 1028.40 MPa, in the nonoxidised alloy, this value was 1027.20 MPa. It is seen that the peak stresses of both materials are close to each other, and the result of the oxidised alloy is slightly better. When we look at the breaking strain to characterise the deformation behaviour in the materials, it is 0.084 mm/mm in the oxidised alloy; In the nonoxidised alloy, it is 0.066 mm/mm. When we look at the stress at offset yield of the two alloys, it is 694.56 MPa in the oxidised alloy; it was found to be 674.092 MPa in the nonoxidised alloy. According to their compressive test properties, the maximum compressive strength is 2164.32 MPa in the oxidised alloy; in the nonoxidised alloy, it is 1531.52 MPa. While the yield strength is 972.50 MPa in oxidised Titanium Grade 5, it was found to be 934.16 MPa in nonoxidised Titanium Grade 5. When the compressive deformation oxidised alloy is 100.01%, in the nonoxidised alloy, it is 68.50%. According to their tribological properties, the oxidised alloy provided the least weight loss after 10,000 m and had the best wear resistance. This material's weight loss and wear coefficient at the end of 10,000 m are 0.127 +/- 0.0002 g and (63.45 +/- 0.15) x 10-8 g/Nm, respectively. The highest weight loss and worst wear resistance have been observed in the nonoxidised alloy. The weight loss and wear coefficients at the end of 10,000 m are 0.140 +/- 0.0003 g and (69.75 +/- 0.09) x 10-8 g/Nm, respectively. The oxidation process has been shown to improve the tribological properties of Titanium Grade 5 alloy.Öğe Effect of Rare Earth Elements (Y, La) on Microstructural Characterization and Corrosion Behavior of Ternary Mg-Y-La Alloys(Mdpi, 2023) Alwakwak, Mohamed Ali Ibrahim; Esen, Ismail; Ahlatci, Hayrettin; Keskin, EsmaIn this study, the microstructural properties and corrosion behavior of RE elements (Y, La) added to magnesium in varying minors after casting and homogenization heat treatment were investigated. Three-phase structures, such as & alpha;-Mg, lamellae-like phases, and network-shaped eutectic compounds, were seen in the microstructure results. The dendrite-like phases were evenly distributed from the eutectic compounds to the interior of the & alpha;-Mg grains, while the eutectic compounds (& alpha;-Mg + Mg) RE (La/Y)) were distributed at the grain boundaries. According to the corrosion results, the typical hydroxide formation for lanthanum content caused the formation of crater structures in the material, and with the increase in lanthanum content, these crater structures increased both in depth and in density. In addition, the corrosion products formed by Y2O3 and Y(OH)(3) in the Mg-3.21Y-3.15 La alloy increased the thickness of the corrosion film and formed a barrier that protects the material against corrosion. The thinness of the protective barrier against corrosion in the Mg-4.71 Y-3.98 La alloy is due to the increased lanthanum and yttrium ratios. In addition, the corrosion resistance of both Mg-3.21Y-3.15 La and Mg-4.71 Y-3.98 La alloys decreases after homogenization. This negative effect on corrosion is due to the coaxial distribution of oxide/hydroxide layers formed by yttrium and lanthanum after homogenization.Öğe Microstructural Characterization, Tribological and Corrosion Behavior of H111 Hot-Rolled AA5754 after Homogenization and Aging(Mdpi, 2024) Abukhdair, Otman Farj Mohammed; Esen, Ismail; Ahlatci, Hayrettin; Keskin, EsmaIn this study, the microstructural properties, wear resistance, and corrosion behavior of H111 hot-rolled AA5754 alloy before heat treatment, after homogenization, and after aging were examined. The microstructure was mainly composed of the scattered forms of black and gray contrast particles on the matrix and precipitations were observed at the boundaries of the grain. The as-rolled material exhibited a dense pancake-shaped grain structure, which is typical of as-rolled material. Observation along the L-direction did not yield distinct demarcations among the grains and was not uniformly distributed, with precipitates at the grain boundary. When they aged, there was a parallel increase in fine and huge black and gray contrast particles in the zone. Therefore, it could be stated that the amount of fine grains increased due to the rise in the homogenization process. The rolled base metal with the grain orientation was found to be parallel to the rolling direction. On the other hand, the coarse grains were clearly observed in the aging heat-treatment condition. The grains had an elongated morphology consistent with the rolling process of the metal before the heat-treatment process. The aged alloy had the highest hardness with a value of 86.83 HB; the lowest hardness was seen in the alloy before heat treatment with a value of 68.67 HB. The weight loss and wear rate of this material at the end of 10,000 m were, respectively, 1.01 x 10-3 g and 5.07 x 10-9 g/Nm. It was observed that the alloy had the highest weight loss and worst wear resistance before heat treatment. Weight loss and wear rates at the end of 10,000 m were, respectively, 3.42 x 10-3 g and 17.08 x 10-9 g/Nm. According to these results, the friction coefficients during wear were parallel and the material with the lowest friction coefficient after aging was 0.045. While the alloys corroded after aging showed more weight loss, the alloys corroded before heat treatment exhibited better corrosion behavior. Among the alloys, the least weight loss after 24 h was observed in the alloy that was corroded before heat treatment and this value was 0.69 x 10-3 mg/dm2. The highest weight loss was observed in the aged alloy with a value of 1.37 x 10-3 mg/dm2. The alloy before heat treatment, which corroded after casting, showed the lowest corrosion rate with a value of 0.39 x 10-3 mg/(dm2day) after 72 h. The alloy that was corroded before heat treatment showed the best corrosion behavior by creating a corrosion potential of 1.04 +/- 1.5 V at a current density of -586 +/- 0.04 mu A/cm2. However, after aging, the corroded alloy showed the worst corrosion behavior with a corrosion potential of 5.16 +/- 3.3 V at a current density of -880 +/- 0.01 mu A/cm2.
